Patient immersion and support surface life determination using RADAR and RFID

ABSTRACT

A patient support system for supporting a patient includes a core support structure which includes supportive foam. The support structure has an upper surface and a lower surface. A radar apparatus, including at least one antenna situated beneath the upper surface and spatially separated therefrom, is adapted to emit a pulse which travels through the support structure and is reflected, by either the upper surface or a surrogate thereof, as a reflected signal back to the radar antenna. The emitted pulse and reflected signal comprise a ranging signal. The patient support system also includes circuitry that determines a life parameter of the core support structure as a function of at least the ranging signal. The patient support system also includes an RFID tag having a memory. The RFID tag is in communication with the circuitry.

The present application is a Continuation in Part of U.S. patentapplication Ser. No. 16/018,316 filed on Jun. 26, 2018 which claims thebenefit, under 35 U.S.C. § 119(e), of U.S. Provisional Application No.62/531,440, filed Jul. 12, 2017, and U.S. Provisional Application No.62/645,495, filed Mar. 20, 2018, each of which is hereby incorporated byreference herein in its entirety.

BACKGROUND

The present disclosure relates to patient support surfaces such asmattresses used on patient beds as well as pads used on chairs,stretchers, surgical tables, examination tables, and other types ofpatient support systems. More particularly the present disclosurerelates to patient support surfaces having immersion sensors.

Patient support surfaces such as air mattresses and other types ofpatient support pads having sensors to determine an amount of immersionof a patient into the patient support surface are known. See, forexample, U.S. Pat. Nos. 5,560,374; 6,009,580; 6,034,526; 6,079,068;6,244,272; 6,560,804; and 9,468,307 in this regard. In general, the morea patient immerses into a mattress or pad, the greater the contact areabetween the patient and the support surface thereby reducing interfacepressure between the patient and the support surface. Such prior artimmersion sensors oftentimes rely upon principles of inductance and/orcapacitance to measure a distance between upper and lower conductivesheets or coils. Having a conductive component at an upper surface of amattress or lining the inside of an upper layer of a mattress with aconductive layer has a tendency to degrade the interface pressureperformance of the mattress in the area of the conductive material. Insome prior art embodiments, the conductive components are provided in asublayer of a mattress that is beneath an upper air layer of themattress and then assumptions are made as to the immersion depth of thepatient based on an amount of compression of the sublayer.

In many of the prior art devices, the immersion sensors are located onlyin a seat region of a mattress beneath the patient's buttocks and areused to optimize the mattress inflation using a single measure of thepatient immersion through the underlying air layer and/or, in somecases, foam layer. The risk of bottoming out increases as a head sectionof a bed frame is raised, for example, due to more of the patient'sweight bearing downwardly through the buttocks onto the seat region ofthe mattress. In such prior art devices, the immersion depth of otherportions of a patient's body, such as the head, shoulder blades, andheels, are not detected. Some prior art immersion detection devices havetheir components inside of air bladders of the mattress which introducesmanufacturing complexities and expense to the mattress. Thus, a needexits for improvements in the use of sensors to detect patient immersionin patient support surfaces.

SUMMARY

An apparatus, system, or method may comprise one or more of the featuresrecited in the appended claims and/or the following features which,alone or in any combination, may comprise patentable subject matter:

According to the present disclosure, a radio detection and ranging(RADAR) apparatus may be configured and may be operated to detect anobject at a range of about 2 centimeters or less, although detection inthe range of about 2 cm to about 100 cm is also contemplated. The RADARapparatus may include at least one RADAR antenna and transceivercircuitry that may be coupled to the at least one RADAR antenna. Thetransceiver circuitry may cooperate with the at least one RADAR antennato emit and subsequently receive a pulse that may have a profile thatsupports detection of the object at the range of about 2 centimeters.The RADAR apparatus may also have processor circuitry that may beconfigured to determine a time-of-flight (TOF) between transmission ofthe pulse and receipt by the at least one RADAR antenna of a reflectedsignal that may be reflected back from the object.

In some embodiments, the object may be comprised primarily of water. Forexample, the object may comprise a person. Alternatively oradditionally, the object may comprise a reflective portion of amattress. The portion may be a reflective layer or small reflectiveobject, such as a piece of foil, metallic threads, etc.

In some embodiments, the at least one RADAR antenna may include at leastone planar antenna. For example, the at least one planar antenna mayinclude at least one spiral antenna to create a circularly polarizedtransmission. Alternatively or additionally, the at least one planarantenna may include at least one Archimedeal spiral broadband antenna.Further alternatively or additionally, the at least one planar antennamay include at least one log-periodic spiral broadband antenna. The atleast one planar antenna may include at least one patch radiatingelement. The at least one planar antenna may include at least oneradiating element.

The RADAR apparatus may further include impedance matching circuitrythat may be configured to tune the at least one antenna to match animpedance of an environment through which the pulse and the reflectedsignal may travel. The environment may include at least a portion of amattress, for example. The portion of the mattress may include at leastone air bladder or may include multiple air bladders or may include atleast one layer of foam or may include at least one microclimatemanagement (MCM) layer or combinations of these bladders and layers.Alternatively or additionally, the environment may include a portion ofa frame of a patient support system. The patient support system mayinclude a bed, a chair, a wheelchair, a stretcher, a surgical table, anexamination table, a patient lift, or an imaging apparatus. In someembodiments, the environment may include a portion of a frame of apatient support system and a portion of a mattress supported by theframe.

Optionally, the RADAR apparatus may further include an impedance-matcheddelay line that may be coupled to the impedance matching circuitry andto the at least one RADAR antenna. The impedance-matched delay line mayincrease an amount of time that it takes for the reflected signal toreturn to the impedance matching circuitry after the transmitted signalwas generated thereby preventing interference between the emitted pulseand the reflected signal. The impedance-matched delay line may include,for example, one or more of the following: a radio frequency (RF) cable,a coaxial cable, an RF transmission line, an RF trace on a printedcircuit board, a printed circuit board microstrip, or a waveguide.

The RADAR apparatus may further include at least one antenna feed to theat least one RADAR antenna and the at least one antenna feed maycomprise a balun. The balun may comprise an infinite balun or a taperedbalun, for example.

In some embodiments, the at least one antenna may include a transmitterantenna that emits the pulse and a receiver antenna that receives thereflected signal. Optionally, the transmitter antenna and the receiverantenna may be coupled to an integrated circuit chip that contains thetransceiver circuitry and the processor circuitry. In some embodiments,the processor circuitry may determine a distance between the at leastone antenna and the object based on averaging raw RADAR data of multiplereflected signals received over a period of time. Alternatively oradditionally, the processor circuitry may determine a distance betweenthe at least one antenna and the object based on multiple TOFdeterminations. For example, the distance d may be based on the formulaTOF=2×d/c where c is the speed of light. Thus, d=TOF×c/2. In someembodiments, a measurement may be made that is linearly proportional tothe distance. For example, to compensate for a slant range created bythe spacing between the transmitter antenna and the receive antenna, thelinear proportional distance may be d×cos(angle) or d×sin(angle) toconvert the slant range into vertical distance if the transmitterantenna and receive antenna are looking at an angle toward the object.

In some embodiments, the processor circuitry may use pulse-pairprocessing to compare phases of successive reflected signals and toignore any reflected signals that do not exhibit a phase shift from aprior reflected signal. Alternatively or additionally, the processorcircuitry may use background subtraction to subtract data received whenno object is present from the reflected signal received when the objectis present. Optionally, the at least one RADAR antenna may include anarray of RADAR antennae. For example, the array of RADAR antennae mayinclude a phased-grid array of RADAR antennae.

In some embodiments, the processor circuitry may implement a Dopplerfilter to accept reflected signals within a desired frequency range andto reject other reflected signals. The Doppler filter may be configuredas a band pass filter to accept reflected signals between a lowerfrequency threshold and an upper frequency threshold. Alternatively, theDoppler filter may be configured as a low pass filter to acceptreflected signals that have a frequency less than a predeterminedthreshold. Further alternatively, the Doppler filter may be configuredas a high pass filter to accept reflected signals that have a frequencygreater than a predetermined threshold.

According to another aspect of the present disclosure, a method ofreducing bedsores and improving clinical workflow may be provided. Themethod may include determining with a radio detection and ranging(RADAR) system a time-of-flight (TOF) or a distance from the patient toa bottom of a patient support system so as to maintain an immersiondepth of the patient on the patient support system within a tolerancerange that may achieve optimal interface pressure between the patientand the patient support system. The tolerance range may be based onupper and lower TOF thresholds, or upper and lower distance thresholds,or both.

In some embodiments, the method may include providing the TOF ordistance to a remote server. If desired, the method may includeadjusting the patient support system as a function of the TOF ordistance. For example, adjusting the patient support system may includelowering a head section of a bed frame of the patient support system.Alternatively or additionally, adjusting the patient support system mayinclude inflating or deflating a bladder of a mattress of the patientsupport system. The method may include notifying a clinician if the TOFor distance is less than a threshold.

In some embodiments, the method may include determining patient motionwith the RADAR system. The method may further include providing patientmotion information to the clinician. The method may include causingpatient motion by changing inflation pressures of various bladderssupporting the patient. Optionally, the method may include providingpatient motion information to a remote server.

According to a further aspect of the present disclosure, a patientsupport system may include a patient support structure to support apatient, control circuitry that may be coupled to the patient supportstructure, and at least one radio detection and ranging (RADAR)apparatus that may be coupled to the patient support structure. Thecontrol circuitry may provide power to the at least one RADAR apparatusand may receive data from the at least one RADAR apparatus. The controlcircuitry may perform at least one function in response to the data thatmay be received from the at least one RADAR apparatus.

In some embodiments, the patient support structure may include one ormore air bladders and the at least one function may include changinginflation of the one or more air bladders. The at least one RADARapparatus may include at least one RADAR antenna and changing inflationof the one or more air bladder may include deflating the one or more airbladders to lessen a distance between the patient and the at least oneRADAR antenna. Alternatively or additionally, the at least one RADARapparatus may include at least one RADAR antenna and changing inflationof the one or more air bladder may include inflating the one or more airbladders to increase a distance between the patient and the at least oneRADAR antenna.

The patient support system may include a server that may be separatefrom the patient support structure, the control circuitry, and the atleast one RADAR apparatus and the at least one function may includetransmitting the data to the server. In some embodiments, the server mayaggregate the data received by the control circuitry from the at leastone RADAR system and transmitted by the control circuitry along withposition data relating to a position of one or more components of thepatient support structure, demographic data relating to patientdemographics, and bedsore data relating to clinical results of bedsores.The patient demographics may include one or more of the following:patient condition such as being of limited mortality, patient diseasehistory, patient height, patient weight, or age of the patient.

In some embodiments, the at least one RADAR apparatus may be configuredto determine a heart rate (HR) and a respiration rate (RR) of thepatient. For example, the at least one RADAR apparatus may use Dopplershift information to determine the HR and the RR. Alternatively oradditionally, the at least one RADAR apparatus may useballistocardiography to determine the HR and the RR. Optionally, the atleast one RADAR apparatus may detect chest movement due to a heartbeatof the patient to determine the HR. Optionally, the at least one RADARapparatus detects diaphragm movement of the patient to determine the RR.

In some embodiments, the control circuitry may be configured todetermine a heart rate (HR) and a respiration rate (RR) of the patientbased on the data received from the at least one RADAR apparatus. Forexample, the control circuitry may use the data from the at least oneRADAR apparatus to determine Doppler shift information to determine theHR and the RR. Alternatively or additionally, the control circuitry mayuse the data from the at least one RADAR apparatus to performballistocardiography to determine the HR and the RR. Optionally, thecontrol circuitry may use the data from the at least one RADAR apparatusto detect chest movement due to a heartbeat of the patient to determinethe HR. Optionally, the control circuitry may use the data from at leastone RADAR apparatus to detect diaphragm movement of the patient todetermine the RR.

According to yet another aspect of the present disclosure, a patientsupport system may include a mattress that may have a top surface and abottom surface. The mattress may be configured to support a patient onthe top surface. The patient support system may also have a radiodetection and ranging (RADAR) apparatus that may be operable to measureinformation indicative of a risk of contracting a pressure ulcer due toimproper immersion in at least one location of the mattress.

In some embodiments, the RADAR apparatus may include an array of RADARantennae. The array of RADAR antennae may include a phased-grid array,for example. The array of RADAR antennae may include a static position,static phase, multiplexed array. If desired, at least one or moreantennae of the array of RADAR antennae may be moved mechanicallyrelative to the mattress.

In some embodiments, the patient support system may further include aframe to support the mattress and an antennae holder that may be movablerelative to the frame beneath the bottom surface of the mattress. Theone or more antennae may be carried by the antennae holder. The antennaeholder may include a plate. The patient support system may include aguide that may be coupled to the frame and that may be configured tosupport the plate for movement relative to the frame. The patientsupport system may further include an actuator that may be operated tomove the plate relative to the guide and relative to the frame. Theactuator may include one or more of the following: a lead screw, amotor, a gear reducer, a linkage, a pulley, a sprocket, a cable, a belt,or a chain.

In some embodiments, a portion of the frame may serve as a guide tosupport the plate for movement. The patient support system may includean actuator that may be operated to move the plate relative to theportion of the frame that serves as the guide. The actuator may includeone or more of the following: a lead screw, a motor, a gear reducer, alinkage, a pulley, a sprocket, a cable, a belt, or a chain.

It is within the scope of this disclosure for the one or more antennaecarried by the antennae holder to include three antennae that may besituated and movable beneath a sacral region of the patient supported bythe mattress. Alternatively or additionally, the one or more antennaecarried by the antennae holder may include two antennae that may besituated and movable beneath a back region of the patient supported bythe mattress. Alternatively or additionally, the one or more antennaecarried by the antennae holder may include two antennae that may besituated and movable beneath a heel region of the patient supported bythe mattress.

According to still a further aspect of the present disclosure, a patientsupport surface for supporting a patient may include a core that mayinclude at least one patient support element and a ticking that maysurround the core. The ticking may have an upper layer overlying thecore and a lower layer underlying the core. The patient support surfacemay also have at least one radio detection and ranging (RADAR) antennathat may be situated beneath the core, such as between the lower layerof the ticking and the core or beneath both the lower layer of tickingand the core. The at least one RADAR antenna may emit a pulse thattravels through the core and that may be reflected by either the patientor an inner surface of the upper layer of the ticking as a reflectedsignal back to the at least one RADAR antenna. The patient supportsurface also may include processor circuitry that may determine atime-of-flight (TOF) of the pulse and the reflected signal to determinewhether the patient supported on the patient support surface is at riskof contracting pressure ulcers due to improper immersion into thepatient support surface.

In some embodiments, the at least one RADAR antenna may include at leastone planar antenna. For example, the at least one planar antenna mayinclude at least one spiral antenna to create a circularly polarizedtransmission. Alternatively or additionally, the at least one planarantenna may include an Archimedeal spiral broadband antenna.Alternatively or additionally, the at least one planar antenna mayinclude a log-periodic spiral broadband antenna.

In some embodiments, the patient support surface may further include animpedance matching circuit that may be configured to tune the at leastone antenna to match an impedance of the core. The patient supportsurface may include at least one antenna feed to the at least one RADARantenna. The at least one antenna feed may comprise a balun. The balunmay comprise an infinite balun or a tapered balun, for example. Thepatient support surface may include at least one radio frequency (RF)driver circuit and the balun may be configured to provide impedancematching from the at least on RF driver circuit to the at least oneRADAR antenna. Other impedance matching circuits, such as a PI filtermay be used. Such a matching filter may be implemented using discretecomponents or transmission line elements.

In some embodiments, the patient support surface may include drivercircuitry that may be coupled to the at least one RADAR antenna.Optionally, the driver circuitry may cooperate with the at least oneRADAR antenna to emit a pulse that may have a period in the range ofabout 0.55 nanoseconds (ns) to about 0.2 ns which are pulse lengthstypical of ultra-wide band (UWB) pulses. Such a short pulse may permitobjects within 2 centimeters of the at least one RADAR antenna to bedetected.

In some embodiments, the patient support surface may include impedancematching circuitry that may be configured to tune the at least one RADARantenna to match an impedance of an environment through which the pulseand the reflected signal travel. The environment may include at least aportion of the at least one patient support element of the core and aportion of the ticking, for example. The at least one patient supportelement may include an air bladder or multiple air bladders.Alternatively or additionally, the at least one patient support elementmay include at least one layer of foam. The environment may include aportion of a panel that supports at least a portion of the patientsupport surface or a portion of a frame of a patient support system thatsupports the patient support surface. For example, the patient supportsystem may include a bed, a chair, a wheelchair, a stretcher, a surgicaltable, an examination table, a patient lift, or an imaging apparatus. Ifdesired, the inner surface of the upper layer of ticking may have aRADAR reflective coating.

Optionally, the patient support surface may further include animpedance-matched delay line that may be coupled to the impedancematching circuitry and to the at least one RADAR antenna. Theimpedance-matched delay line may increase an amount of time that ittakes for the reflected signal to reach the impedance matching circuitrythereby preventing interference between the emitted pulse and thereflected signal. The impedance-matched delay line may include, forexample, one or more of the following: a radio frequency (RF) cable, acoaxial cable, an RF transmission line, an RF trace on a printed circuitboard, a printed circuit board microstrip, or a waveguide.

This disclosure contemplates that the at least one antenna may include atransmitter antenna that may emit the pulse and a receiver antenna thatmay receive the reflected signal. In some embodiments, the transmitterantenna and the receiver antenna may be coupled to an integrated circuitthat may contain the driver circuitry and the processor circuitry.Optionally, the transmitter antenna and the receiver antenna may becoupled to an integrated circuit chip by impedance matching circuitry.Such an integrated circuit chip may include the driver circuitry or theprocessor circuitry or both.

In some embodiments, the processor circuitry may use TOF to determine adistance based on averaging raw RADAR data of multiple reflected signalsreceived over a period of time. Alternatively or additionally, theprocessor circuitry may determine a distance based on multiple TOFdeterminations. In some embodiments, the processor circuitry may usepulse-pair processing to compare phases of successive reflected signalsand to ignore any reflected signals that do not exhibit a phase shiftfrom a prior reflected signal. Alternatively or additionally, theprocessor circuitry may use background subtraction to subtract datareceived when no patient is present on the patient support surface fromthe reflected signal received when the patient is present.

In some embodiments of the patient support surface, the at least oneRADAR antenna may include an array of RADAR antennae. The array of RADARantennae may include a phased-grid array of antennae, for example. Ifdesired, the processor circuitry may implement a Doppler filter toaccept reflected signals within a desired frequency range and to rejectother reflected signals. The Doppler filter may be configured as a bandpass filter to accept reflected signals between a lower frequencythreshold and an upper frequency threshold. Alternatively, the Dopplerfilter may be configured as a low pass filter to accept reflectedsignals that have a frequency less than a predetermined threshold.Further alternatively, the Doppler filter may be configured as a highpass filter to accept reflected signals that have a frequency greaterthan a predetermined threshold.

In some embodiments, the core may include one or more air bladders andwherein inflation of the one or more air bladders is changed in responseto the TOF. For example, the one or more air bladders may be changed viadeflation to lessen the TOF. The one or more air bladders may be changedvia inflation to increase the TOF. Thus, the TOF may be controlledwithin a range to prevent the patient from bottoming out but also topermit the patient to immerse into the patient support surfacesufficiently to reduce interface pressures.

In some embodiments, the processor circuitry of the patient supportsurface may be configured to determine a heart rate (HR) and arespiration rate (RR) of the patient based on the TOF of successivepulses. The processor circuitry may use Doppler shift information todetermine the HR and the RR. Alternatively or additionally, theprocessor circuitry may use ballistocardiography to determine the HR andthe RR. If desired, the processor circuitry may detect chest movementdue to a heartbeat of the patient to determine the HR. Alternatively oradditionally, the processor circuitry may detect diaphragm movement ofthe patient to determine the RR.

According to yet a further aspect of the present disclosure, a patientsupport system for supporting a patient may include a mattress that mayinclude a core and a ticking that may surround the core. The ticking mayhave an upper layer overlying the core and a lower layer underlying thecore. The patient support system may have a frame that may include amattress support deck that may support the mattress. At least one radiodetection and ranging (RADAR) antenna may be coupled to the framebeneath the lower layer of ticking. The at least one RADAR antenna mayemit a pulse that may travel through the mattress and that may bereflected by either the patient or an inner surface of the upper layerof the ticking or a portion of an inner surface of the upper layer ofthe ticking (e.g. reflective threads or patches) as a reflected signalback to the at least one RADAR antenna. The patient support system mayhave processor circuitry that may determine a time-of-flight (TOF) ofthe pulse and the reflected signal to determine whether the patientsupported on the patient support surface may be at risk of bottomingout.

In some embodiments, the mattress support deck may include a pluralityof deck sections and the at least one RADAR antenna may be coupled to anupper surface of a first deck section of the plurality of deck sections.Alternatively or additionally, the mattress support deck may include aplurality of deck sections and the at least one RADAR antenna may becoupled to a bottom surface of a first deck section of the plurality ofdeck sections. Thus, the pulse may travel through the first deck sectionand the mattress.

In some embodiments, the at least one RADAR antenna of the patientsupport system may include at least one planar antenna. The at least oneplanar antenna may include, for example, at least one spiral antenna tocreate a circularly polarized transmission. The at least one planarantenna may include an Archimedeal spiral broadband antenna.Alternatively or additionally, the at least one planar antenna mayinclude a log-periodic spiral broadband antenna.

It is within the scope of this disclosure for the patient support systemto include an impedance matching circuit that may be configured to tunethe at least one RADAR antenna to match an impedance of the a portion ofthe mattress through which the pulse and the reflected signal travel. Itis also within the scope of this disclosure for the patient supportsystem to include an impedance matching circuit configured to tune theat least one RADAR antenna to match an impedance of the mattress and aportion of the frame through which the pulse and the reflected signaltravel.

In some embodiments, the patient support system may include at least oneantenna feed to the at least one RADAR antenna and the at least oneantenna feed may include a balun. The balun may include an infinitebalun or a tapered balun, for example. The patient support system mayinclude at least one radio frequency (RF) driver circuit and the balunmay be configured to provide impedance matching from the at least on RFdriver circuit to the at least one RADAR antenna.

Optionally, the patient support system may further include animpedance-matched delay line that may be coupled to the impedancematching circuitry and to the at least one RADAR antenna. Theimpedance-matched delay line may increase an amount of time that ittakes for the reflected signal to reach the impedance matching circuitrythereby preventing interference between the emitted pulse and thereflected signal. The impedance-matched delay line may include, forexample, one or more of the following: a radio frequency (RF) cable, acoaxial cable, an RF transmission line, an RF trace on a printed circuitboard, a printed circuit board microstrip, or a waveguide.

In some embodiments of the patient support system, an inner surface ofthe upper layer of ticking may have a RADAR reflective coating. Ifdesired, the core may include an air bladder. Alternatively oradditionally, the core may include multiple air bladders with at least afirst air bladder situated above a second air bladder. Alternatively oradditionally, the core may include at least one layer of foam.

It is contemplated by this disclosure that the at least one antenna mayinclude a transmitter antenna that may emit the pulse and a receiverantenna that may receive the reflected signal. The transmitter antennaand the receiver antenna may be coupled to an integrated circuit thatmay contain driver circuitry and the processor circuitry. The processorcircuitry may determine a distance between the at least one antenna andthe patient based on averaging raw RADAR data of multiple reflectedsignals received over a period of time. Alternatively or additionally,the processor circuitry may determine a distance between the at leastone antenna and the patient based on multiple TOF determinations.

The processor circuitry of the patient support system may use pulse-pairprocessing to compare phases of successive reflected signals and toignore any reflected signals that do not exhibit a phase shift from aprior reflected signal. Alternatively or additionally, the processorcircuitry may use background subtraction to subtract data received whenno patient is present on the mattress from the reflected signal receivedwhen the patient is present on the mattress. The at least one RADARantenna may comprise an array of RADAR antennae. The array of RADARantennae may include a phased-grid array of antennae.

In some embodiments, the processor may implement a Doppler filter toaccept reflected signals within a desired frequency range and to rejectother reflected signals. The Doppler filter may be configured as a bandpass filter to accept reflected signals between a lower frequencythreshold and an upper frequency threshold. The Doppler filter may beconfigured as a low pass filter to accept reflected signals that have afrequency less than a predetermined threshold. The Doppler filter may beconfigured as a high pass filter to accept reflected signals that have afrequency greater than a predetermined threshold.

In some embodiments of the patient support system, the core may includeone or more air bladders and inflation of the one or more air bladdersmay be changed in response to the TOF. For example, the one or more airbladders may be changed via deflation to permit the patient to furtherimmerse into the mattress. The one or more air bladders may be changedvia inflation to decrease the risk of the patient bottoming out.

In some embodiments of the patient support system, the processorcircuitry may be configured to determine a heart rate (HR) and arespiration rate (RR) of the patient based on the TOF of successivepulses. The processor circuitry may use Doppler shift information todetermine the HR and the RR, for example. Alternatively or additionally,the processor circuitry may use ballistocardiography to determine the HRand the RR. The processor circuitry may detect chest movement due to aheartbeat of the patient to determine the HR. The processor circuitrymay detect diaphragm movement of the patient to determine the RR.

According to another aspect of the present disclosure, a patient supportsurface may include a ticking that may define an interior region betweena top layer of the ticking and a bottom layer of the ticking. At leastone layer of foam material may fill the interior region. A radiodetection and ranging (RADAR) apparatus may be operable to measure adistance toward bottoming out of a patient on the mattress. The RADARapparatus may include at least one RADAR antenna. Processor circuitrymay be provided to determine whether the performance of the at least onelayer of foam material has degraded based on the distance, or based onthe distance and patient weight. Degraded performance is one measure ofthe end of a mattress's end of life.

In some embodiments, the processor circuitry may provide an alert if thedegradation indicates that a useful life of the patient support surfacehas been reached.

According to a further aspect of the present disclosure, a patientsupport surface may include a ticking that may define an interior regionbetween a top layer of the ticking and a bottom layer of the ticking. Atleast one layer of foam material may fill the interior region. A radiodetection and ranging (RADAR) apparatus may have at least one RADARantenna that may emit a pulse that may travel through the foam materialand that may be reflected by either the patient or an inner surface ofthe top layer of the ticking as a reflected signal back to the at leastone RADAR antenna. Processor circuitry may be provided to determine atime-of-flight (TOF) of the pulse and the reflected signal. Theprocessor circuitry may also determine an amount of degradation of thefoam material based on the TOF and based on patient weight.

In some embodiments, the processor circuitry may provide an alert if theamount of degradation exceeds a threshold indicating that a useful lifeof the patient support surface has been reached.

According to still another aspect of the present disclosure, a patientsupport system may include a mattress that may have a top surface and abottom surface. The mattress may be configured to support a patient onthe top surface. A radio detection and ranging (RADAR) apparatus mayhave at least one RADAR antenna that may emit a pulse that may travelthrough the mattress and that may be reflected by either the patient oran inner surface of a material defining the top surface as a reflectedsignal back to the at least one RADAR antenna. Processor circuitry maydetermine a time-of-flight (TOF) of the pulse and the reflected signal.The patient support system may have a frame to support the mattress. Anantenna holder may be movable relative to the frame beneath the bottomsurface of the mattress. The at least one antenna may be carried by theantenna holder.

In some embodiments, the antenna holder may include a plate. The patientsupport system may include a guide that may be coupled to the frame andthat may be configured to support the plate for movement relative to theframe. The patient support system may further include an actuator thatmay be operated to move the plate relative to the guide and relative tothe frame. The actuator may include one or more of the following: a leadscrew, a motor, a gear reducer, a linkage, a pulley, a sprocket, acable, a belt, or a chain.

In some embodiments, a portion of the frame may serve as a guide tosupport the plate for movement. The patient support system may includean actuator that may be operated to move the plate relative to theportion of the frame that serves as the guide. The actuator may includeone or more of the following: a lead screw, a motor, a gear reducer, alinkage, a pulley, a sprocket, a cable, a belt, or a chain.

In some embodiments, the at least one antenna carried by the antennaholder may include three antennae that may be situated and movablebeneath a sacral region of the patient supported by the mattress.Alternatively or additionally, the at least one antenna carried by theantenna holder may include two antennae that may be situated and movablebeneath a back region of the patient supported by the mattress.Alternatively or additionally, the at least one antenna carried by theantenna holder may include two antennae that may be situated and movablebeneath a heel region of the patient supported by the mattress.

According to still a further aspect of the present disclosure, a patientsupport apparatus may include a frame, a mattress that may be supportedby the frame, and an immersion sensor that may be coupled to the frameand that may be located outside of the mattress. The immersion sensormay be operable to determine patient immersion into an upper surface ofthe mattress.

In some embodiments, the immersion sensor may be located underneath themattress. The immersion sensor may include a radio detection and ranging(RADAR) antenna and a bottom surface of the mattress may abut an uppersurface of the RADAR antenna. Optionally, the RADAR antenna may includea housing and a portion of the housing may provide the upper surface.The frame may include a mattress support deck that may include at leastone pivotable deck section and the RADAR antenna may be situated atopthe pivotable deck section.

In some embodiments, the frame may include a mattress support deck thatmay include at least one pivotable deck section and the immersion sensormay include a radio detection and ranging (RADAR) antenna that may belocated beneath the pivotable deck section. For example, the RADARantenna may be coupled to a bottom surface of the pivotable decksection.

In some embodiments, the frame may include an antenna holder that may belocated beneath a bottom surface of the pivotable deck section and theRADAR antenna may be carried by the antenna holder. If desired, theantenna holder may include a plate. The pivotable deck section mayinclude a guide that may be configured to support the plate for movementrelative to the pivotable deck section. The patient support apparatusmay further include an actuator that may be operated to move the plate.The actuator may include one or more of the following: a lead screw, amotor, a gear reducer, a linkage, a pulley, a sprocket, a cable, a belt,or a chain.

As contemplated by some embodiments of this disclosure, the immersionsensor may include a radio detection and ranging (RADAR) antenna, radiofrequency (RF) driver and receiver circuitry, impedance matchingcircuitry that may be coupled to the RADAR antenna and that may becoupled to the RF driver and receiver circuitry, and processor circuitrythat may be coupled to the RF driver and receiver circuitry.

Optionally, the patient support apparatus may further include animpedance-matched delay line that may be coupled to the impedancematching circuitry and to the RADAR antenna. The impedance-matched delayline may increase an amount of time that it takes for a reflected signalto reach the impedance matching circuitry thereby preventinginterference between an emitted pulse and the reflected signal. Theimpedance-matched delay line may include, for example, one or more ofthe following: a radio frequency (RF) cable, a coaxial cable, an RFtransmission line, an RF trace on a printed circuit board, a printedcircuit board microstrip, or a waveguide.

According to yet another aspect of the present disclosure, a system fordetecting time of flight in a patient support system may be provided.The system may include a patient support (bed, chair, table, stretcher,etc), a RADAR that may be integrated into the patient support, anantenna, and an algorithm for determining the time between transmissionand reception of a RADAR pulse.

According to still a further aspect of the present disclosure, amattress end-of-life testing apparatus for use with a mattress may beprovided. The mattress end-of-life testing apparatus may include atleast one RADAR antenna that may be placed beneath the mattress, atleast one test weight that may be placed atop the mattress, andcircuitry that may be coupled to the at least on RADAR antenna and thatmay have an algorithm for determining an amount of time betweentransmission and reception of a RADAR pulse. The amount of time may beused to determine whether the mattress has reached an end of its usefullife.

According to yet still another aspect of the present disclosure, apatient support apparatus may include a patient support frame, a patientsupport surface that may be supported on the patient support frame, anda RADAR system that may be carried by the patient support frame, thatmay be operable to determine a depth to which a patient is immersed intothe patient support surface, and that may be operable to perform aDoppler analysis to determine at least one of a heart rate or arespiration rate of the patient.

In some embodiments, the RADAR system may be operable to determine boththe heart rate and respiration rate of the patient. The RADAR system mayinclude electronically steerable RADAR sensors, for example. Theelectronically steerable RADAR sensors, in turn, may include a pluralityof transmitting antennae and a plurality of receiving antennae. Theplurality of transmitting antennae and the plurality of receivingantennae may be arranged in a grid beneath an upper surface of thepatient support surface. Reflected signals from the plurality oftransmitting antennae may be combined to improve signal-to-noise ratio,change the gain, steer the direction of the beam, and/or to allowscanning of a larger area.

In some embodiments, signals received by the plurality of receivingantennae may be used by the RADAR system for body contour mapping. Thebody contour mapping may be used to determine whether the patient is atrisk of developing pressure ulcers. Alternatively or additionally, thebody contour mapping may be used in connection with determining a Bradenscore for the patient including determining a patient mobilitysub-factor of the Braden score. Micromotion for the patient may bedetermined using, for example, Doppler processing. Further alternativelyor additionally, the body contour mapping may be used in connection withdetermining functional decline of the patient. Still furtheralternatively or additionally, the body contour mapping may be used todetermine a location on the patient support surface of at least one ofthe patient's legs, arms, trunk, pelvis or head.

Optionally, the body contour mapping may be used to determine whetherthe patient is side-lying, lying on their stomach, or lying on theirback. The patient support surface may include one or more air bladdersand inflation of at least one air bladder of the one or more airbladders may be adjusted based on whether the patient is side-lying,lying on their stomach, or lying on their back. Alternatively oradditionally, the body contour mapping may be used to determine whetherthe patient has slid toward a foot end of the patient support surface.The patient support surface may include one or more air bladders andinflation of at least one air bladder of the one or more air bladdersmay be adjusted based on whether the patient has slid toward the footend of the patient support surface or whether the patient is in a properposition on the patient support apparatus. If desired, the body contourmapping may be used to determine sleep quality of the patient, forexample by analyzing movement and/or respiration. Alternatively oradditionally, the body contour mapping may be used to determineimpending exit of the patient from the patient support apparatus.

In some embodiments, the RADAR system may be operable to determine adistance to the patient or to a surface of the patient support surfaceadjacent the patient for each receiving antenna of the plurality ofreceiving antennae by using (i) a time-of-flight (TOF) betweentransmission of pulses from the plurality of transmitting antennae andreceipt by the plurality of receiving antennae of a reflected signalthat is reflected back from the patient or reflected back from thesurface of the patient support surface adjacent the patient, (ii)antenna beam angle and geometry, and (iii) signal strength.

The present disclosure contemplates that the Doppler analysis todetermine at least one of a heart rate or a respiration rate of thepatient may include a micro-Doppler analysis that may determine a phasechange between first signals that may be transmitted by the plurality oftransmitting antennae and second signals that may be received by theplurality of receiving antennae. The Doppler analysis may be used todetermine one or more of the following: premature ventricularcontractions (PVC's) of the patient's heart; rate-based arrhythmias ofthe patient's heart; lethal arrhythmias of the patient's heart; onset ofcongestive heart failure; or progression of congestive heart failure.Alternatively or additionally, the Doppler analysis may be used todetect apnea and/or obstructive sleep apnea of the patient.

In some embodiments, the RADAR system may include a local oscillator, apower splitter that may have an input coupled to the local oscillator,and at least one transmitting antenna that may be coupled to a firstoutput of the power splitter. The RADAR system may further have a mixerthat may include a first input that may be coupled to a second output ofthe power splitter and at least one receiving antenna that may becoupled to a second input of the mixer. A first low pass filter of theRADAR system may have an input that may be coupled to a quadratureoutput of the mixer and a second low pass filter of the RADAR system mayhave an input that may be coupled to an in-phase output of the mixer.The RADAR system may further have a first analog-to-digital converterthat may be coupled to an output of the first low pass filter and asecond analog-to-digital converter that may be coupled to an output ofthe second low pass filter. It is contemplated by this disclosure thatthe RADAR system may be instantiated as a system-on-chip.

Additional features, which alone or in combination with any otherfeature(s), such as those listed above and those listed in the claims,may comprise patentable subject matter and will become apparent to thoseskilled in the art upon consideration of the following detaileddescription of various embodiments exemplifying the best mode ofcarrying out the embodiments as presently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the accompanyingfigures, in which:

FIG. 1 is a block diagram showing a patient support system having aradio detection and ranging (RADAR) apparatus integrated therein (insolid) and having one or more optional additional RADAR apparatusesintegrated therein (in phantom); the RADAR apparatus including a RADARantenna, impedance matching circuitry, RF driver/receiver circuitry, andprocessor circuitry; the RADAR apparatus coupled to control circuitrywhich signals a pneumatic system to adjust inflation of one or more airbladders and/or which signals one or more actuators to move movableportions of the patient support system based on a distance, d, or atime-of-flight of a pulse and return signal, between the RADAR antennaand an object or target as determined by the RADAR apparatus;

FIG. 2 is a block diagram showing an alternative embodiment of the RADARapparatus of FIG. 1, the alternative embodiment RADAR apparatus having aRADAR transmit antenna and a RADAR receive antenna separate from theRADAR transmit antenna, impedance matching circuitry coupled to theRADAR transmit and receive antennae, RF driver circuitry and receivercircuitry coupled to the impedance matching circuitry, and processorcircuitry coupled to the RF driver circuitry and receiver circuitry, theRF driver circuitry and the processor circuitry optionally packaged asan integrated circuit (in phantom);

FIG. 3 is a block diagram showing a second alternative embodiment of theRADAR apparatus of FIG. 1, the second alternative embodiment RADARapparatus having multiple RADAR antennae and multiple correspondingimpedance matching circuitry and a multiplexer to select which of theRADAR antennae are active, the multiplexer being coupled to RFdriver/receiver circuitry (aka RF transceiver circuitry) which is sharedby the multiple RADAR antennae and processor circuitry which is coupledto the RF transceiver circuitry and which is shared by the multipleRADAR antennae;

FIG. 4 is a top plan view of an Archimedean spiral antenna which issuitable for use in connection with the RADAR apparatus of the patientsupport system of FIG. 1;

FIG. 5 is a top plan view of log-periodic spiral antenna which issuitable for use in connection with the RADAR apparatus of the patientsupport system of FIG. 1;

FIG. 6 is perspective view of an infinite balun, in the form of acoaxial cable, which is included in the impedance matching circuitry ofFIG. 1 in some embodiments, coupled to a spiral antenna, the coaxialcable having its center conductor coupled to a first arm of a pair ofarms of the spiral antenna, and the coaxial able having its outerconductor coupled to a second arm of the pair of arms of the spiralantenna;

FIG. 7 is a top plan view of a second embodiment of an infinite balunshowing a coaxial cable extending from a radio (e.g., RF driver/receivercircuitry of FIG. 1) and spiraled to form a first arm of a pair of armsof a spiral antenna, the coaxial cable having its center conductorcoupled to a second arm of the pair of arms of the spiral antenna, thecoaxial cable of the second embodiment serving as a portion of the RADARantenna and a portion of the impedance matching circuitry of FIG. 1;

FIG. 8 is a perspective view of a portion of a tapered balun, in theform of a coaxial cable, which is included in the impedance matchingcircuitry of FIG. 1 in some embodiments, showing an outer conductor ofthe coaxial having a tapered notch with an end region of the outerconductor formed into a transmission line that is balanced with a centerconductor of the coaxial cable;

FIG. 9 is perspective view of another embodiment of a portion of atapered balun, in the form of a microstrip transmission line, which isincluded in the impedance matching circuitry of FIG. 1 in someembodiments, showing a top strip of the tapered balun having uniformwidth along its length and a bottom strip having a wide portion thattapers down to an end portion having a substantially equivalent width asthe top strip so as to form a balanced transmission line at the endportion of the tapered balun;

FIG. 10A is a cross sectional view showing a portion of an air mattress,a portion of a patient supported by the air mattress, and a portion of aframe (in phantom) of a patient support apparatus that supports the airmattress, the air mattress having a RADAR antenna sandwiched between abottom ticking layer of the air mattress and a base foam layer of theair mattress, an inflatable bladder above the base foam layer, and a toplayer of ticking between the inflatable air bladder and the patient, andalso showing an optional RADAR reflective coating (in phantom) on aninside surface at a top of the inflatable air bladder;

FIG. 10B is a cross sectional view, similar to FIG. 10A but having thefoam layer removed, showing that the RADAR antenna is sandwiched betweenthe bottom ticking layer and the inflatable bladder resulting in amattress of reduced vertical thickness as compared to the mattress ofFIG. 12A;

FIG. 10C is a cross sectional view, similar to FIG. 10A, showing analternative embodiment of a mattress having a lower inflatable airbladder situated atop the base foam layer, a set of three upper bladderssituated atop the lower inflatable bladder, and a microclimatemanagement layer above the upper bladders;

FIG. 11A is an exploded view of a portion of a patient support apparatusshowing a mattress and an articulated mattress support deck of a frameof the patient support apparatus spaced downwardly from the mattress, anupper surface of a head section of the mattress support deck having twoRADAR antennae coupled thereto, an upper surface of a seat section ofthe mattress support deck having three RADAR antennae coupled thereto,and an upper surface of a foot section of the mattress support deckhaving two RADAR antennae coupled thereto;

FIG. 11B is a cross sectional view of a foam mattress showing that theRADAR antenna is situated between a bottom ticking layer of the foammattress and a frame of a patient support apparatus;

FIG. 12 is an exploded view of a portion of a patient support apparatus,similar to FIG. 11A, showing a mattress and an articulated mattresssupport deck of a frame of the patient support apparatus spaceddownwardly from the mattress, a bottom surface of a head section of themattress support deck having two RADAR antennae coupled thereto, abottom surface of a seat section of the mattress support deck havingthree RADAR antennae coupled thereto, and a bottom surface of a footsection of the mattress support deck having two RADAR antennae coupledthereto;

FIG. 13 is a bottom plan view of a mattress support deck, similar to themattress support decks of FIGS. 11A and 12, showing the head, seat, andfoot sections of the mattress support deck having movable plates coupledthereto, each movable plate carrying respective RADAR antennae and beingmovable along a longitudinal dimension of the mattress support deck toreposition the RADAR antennae in response to the operation of respectiveactuators (shown diagrammatically in FIG. 15);

FIG. 14 is a perspective view of a portion of the mattress support deckof FIG. 15 showing C-shaped guides mounted to respective side framemembers of the respective section of the mattress support deck, theguides receiving respective opposite ends of the movable plate therein,the actuator for moving the movable plate including a threaded jackscrew extending through a threaded nut mounted to a bottom surface ofthe movable plate and a motor/gear reducer unit mounted to an end framemember and coupled to the jack screw, the motor/gear reducer unit beingoperable to rotate the jack screw to move the movable plate along theguides;

FIG. 15 is a bottom plan view of a deck section of the mattress supportdeck of FIG. 15 showing a first alternative actuator for moving themovable plate, the first alternative actuator including a flexibletether (e.g., cable, band, belt, or chain) trained around a motorizeddrive wheel (e.g., pulley or sprocket) and an idler wheel (e.g., pulleyor sprocket), one flight of the flexible tether being anchored to themovable plate such that rotation of the motorized drive wheel by acorresponding motor moves the movable plate along the guides;

FIG. 16 is a bottom plan view of a deck section of the mattress supportdeck, similar to FIG. 15, showing a second alternative actuator formoving the movable plate, the second alternative actuator including amulti-stage scissors linkage interconnected between an end frame memberof the deck section and the movable plate, a motor being mounted to theend frame member and operable to pivot a main link of the scissorslinkage to extend and retract the scissors linkage to move the movableplate along the guides;

FIG. 17 is a block diagram showing a portion of a RADAR apparatus,similar to FIG. 1, but having an impedance-matched delay lineinterconnecting the RADAR antenna and the impedance matching circuitry;

FIG. 18 is a block diagram of a RADAR apparatus or system showing theRADAR system including a local oscillator, a power splitter having aninput coupled to the local oscillator, at least one transmitting antennacoupled to a first output of the power splitter, a mixer having a firstinput coupled to a second output of the power splitter, at least onereceiving antenna coupled to a second input of the mixer, a first lowpass filter having an input coupled to a quadrature output of the mixer,a second low pass filter having an input coupled to an in-phase outputof the mixer, a first analog-to-digital converter coupled to an outputof the first low pass filter, and a second analog-to-digital convertercoupled to an output of the second low pass filter; and

FIG. 19 includes a pair of graphs showing an electrocardiograph signalin an upper graph and a phase graph in the lower graph with R-wavearrows indicating correspondence between R-wave spikes in the upper andlower graphs to indicate that the phase measured by the RADAR apparatusof FIG. 18 is usable to determine heart rate of a patient.

FIG. 20 is a plot relating a quantification of mattress life status LSto a time stamp for patients of different weight classes.

FIG. 21 is a schematic elevation view of a mattress showing the verticaldistance d between a radar antenna and the top surface of the mattressat earlier and later times in the mattress's life.

FIG. 22 is a graph relating time of flight of a radar signal to thevertical distances of FIG. 21 (right side scale) and to the remaininglife of the mattress (left side scale).

FIG. 23 is a block diagram showing a sequence of actions for making anassessment of the life status of a mattress.

FIG. 24 is a graph showing deformation versus time of the mattress ofFIG. 21, the graph having a time constant τ.

FIG. 25 is an example of a relationship between remaining life of thefoam components of the mattress of FIG. 21 and a time constant τ, suchas the time constant associated with the graph of FIG. 24, in whichhigher values of τ indicate longer remaining life.

FIG. 26 is an example of a relationship between remaining life of thefoam components of the mattress of FIG. 21 and a time constant τ, suchas the time constant associated with the graph of FIG. 24, in whichhigher values of τ indicate shorter remaining life.

FIG. 27 is a block diagram similar to FIG. 23 showing a differentsequence of actions for making the assessment of remaining life.

FIG. 28 is an elevation view showing a patient support system whichincludes a frame, a mattress (more generally referred to as a coresupport structure), a ticking which envelops the mattress, an RFID tag,an RFID reader, and a radar system whose components are completelyoutside the core support structure and ticking.

NOTE: FIGS. 27-30. The RFID reader may be external (carried by a serviceperson to make measurements).

FIG. 29 is a view similar to FIG. 28 in which the components of theradar system are inside the ticking.

FIG. 30 is a view similar to FIG. 28 in which the components of theradar system are distributed such that some components are inside theticking and some are outside the ticking.

FIG. 31 is a diagram similar to FIG. 1 showing possible relationshipsbetween life determination circuitry and other circuitry alreadyillustrated in FIG. 1.

FIG. 32 is a view showing a hand held, portable RFID reader which may becarried from place to place by a user thereof.

FIG. 33 is a block diagram showing one example of how the RFID tag shownin other drawings and described elsewhere in this specification may beemployed.

FIG. 34 is a schematic of components involved in the actions of FIG. 33.

FIG. 35 is a diagram showing examples of how life parameters of the coresupport structure may be determined as a function of a radar rangingsignal or a property thereof.

FIG. 36 is a flow chart showing another example of how the RFID tagshown in other drawings and described elsewhere in this specificationmay be used.

FIG. 37 is a plot of the numerical values of two parameters of a radarranging signal and their associated time stamps.

FIG. 38 is an example of a core support structure usage log that may bestored in an RFID memory and whose entries are not necessarily relatedto any particular event that might have a bearing on the life status ofthe core support structure.

FIG. 39 is a plot showing the deterioration profile of the core supportstructure (expressed as remaining life versus time stamp) based on thedata from the usage log of FIG. 38.

FIG. 40 is a plot showing the deterioration rate of the core supportstructure versus time stamp based on the data from the usage log of FIG.38.

FIG. 41 is an example of a core support structure usage log similar tothat of FIG. 38 but whose entries are related to events believed to havea bearing on the life status of the core support structure.

DETAILED DESCRIPTION

According to some embodiments of the present disclosure, one or moreradio detection and ranging (RADAR) apparatuses are integrated into apatient support system and are used to determine patient immersion, orstated more accurately, to determine a risk of a patient bottoming outon a patient support surface of the patient support system. The RADARapparatuses disclosed herein measure a time-of-flight (TOF) of a RADARpulse which, if desired, can be used to calculate a distance between atleast one RADAR antenna and an object of interest, such as the patient.The TOF or distance is used in some contemplated embodiments to controlbladder inflation and deflation to maintain the patient within a desiredimmersion depth between upper and lower tolerance range limits. Thetolerance range limits are upper and lower TOF thresholds, or upper andlower distance thresholds, or both. By maintaining the patient at thedesired immersion depth, while preventing bottoming out of the patient,the interface pressure between the patient and the surface supportingthe patient is maintained at optimum values.

While all types of patient support systems are contemplated herein, someexamples of a patient support system include a standalone mattresssystem, a mattress overlay, a patient bed, a patient bed with anintegrated mattress system, a surgical table, an examination table, animaging table, a stretcher, a chair, a wheelchair, and a patient lift,just to name a few. Patient support surfaces contemplated herein includeair mattress, foam mattresses, combination air and foam mattresses,mattress overlays, surgical table pads and mattresses, stretcher padsand mattresses, chair pads, wheelchair pads, and patient lift pads, justto name a few.

As shown diagrammatically in FIG. 1, a patient support system 10includes one or more RADAR antenna 12 which are operated to emit a pulse14 generally upwardly toward a target or object 16. In some embodiments,the object 16 is a patient situated atop a patient support surface, suchas a mattress or pad, of the patient support system 10. Patients arecomprised primarily of water. The pulse 14 is reflected by the object 16as a reflected signal 18 which is detected or read by RADAR antenna 12.Losses, such as absorbed and refracted energy, are indicateddiagrammatically in FIG. 1 with squiggly arrows.

Patient support system 10 includes radio frequency (RF) driver andreceiver circuitry 20 coupled to each respective RADAR antenna 12 bycorresponding impedance matching circuitry 22 as shown diagrammaticallyin FIG. 1. RF driver/receiver circuitry is sometimes referred to hereinas RF transceiver circuitry. The RF driver portion of circuitry 20operates to provide a pulse of electrical energy (i.e., current andvoltage) via impedance matching circuitry 22 to cause the RADAR antenna12 to emit the pulse 14. The receiver portion of circuitry 20 receivesthe reflected signal 18 from RADAR antenna 12 via impedance matchingcircuitry 22.

Patient support system also includes processor circuitry 24 coupled torespective RF driver/receiver circuitry 20. One or more of RADAR antenna12 and circuitry 20, 22, 24 is considered to be a RADAR apparatus orRADAR system according to this disclosure. In some embodiments, thereceiver portion of circuitry 20 or the processor circuitry 24 includesan analog-to-digital converter (ADC) to convert the received analogreflected signal 18 into digital data. In some embodiments, circuitry 20sends to processor circuitry 24 data indicative of atime-of-transmission of pulse 14 and a time-of-arrival of reflectedsignal 18 by RADAR antenna 12. The difference between thetime-of-transmission and time-of-arrival is the time-of-flight (TOF) ofpulse 14 and signal 18. The TOF is determined by processor 24 in someembodiments and is determined by circuitry 20 in other embodiments. Inthose embodiments in which circuitry 20 calculates the TOF, it is outputto processor circuitry 24 from circuitry 20.

Processor circuitry 24 uses the TOF data to determine whether theobject, sometimes referred to herein as “the patient 16,” is at risk ofbottoming out. Bottoming out, sometimes referred to herein as just“bottoming,” refers to a condition in which a patient or other weight ontop of a mattress or pad compresses the top of the mattress or pad untilit reaches its lowest point, i.e., it cannot be compressed any farther.At that point, there is little to no further cushioning and the mattressor pad would feel hard and uncomfortable to the patient. Thus, the riskfor the patient 16 to develop pressure ulcers increases greatly if thepatient bottoms out on a mattress or pad. Alternatively or additionally,processor circuitry 24 uses the TOF data to set or adjust bladderpressures for optimal immersion of the patient into the mattress or padto reduce interface pressure (IFP) between the patient and the uppersurface of the mattress or pad. The optimal immersion is considered tooccur if the TOF data is within a tolerance range between upper andlower TOF thresholds.

In some embodiments, the TOF data may be used directly by processorcircuitry 24 to determine whether the patient is at risk of bottomingout. In such embodiments, the TOF data is compared to a TOF threshold tomake the determination. In other embodiments, a distance, d, shown inFIG. 1, between RADAR antenna 12 and the patient 16 is calculated basedon the TOF and then the distance, d, is compared to a distancethreshold. The TOF and distance, d, are related mathematically in thatTOF=2×d/c where c is the speed of light. Thus, d=TOF×c/2. Thus, TOF ordistance, d, can be compared to a threshold to determine how close thepatient 16 is to bottoming out.

According to this disclosure, the pulse 14 is very short in duration sothat patients within about 2 centimeters (cm) or less of bottoming outcan be detected. Of course, at the option of the system designer, athreshold greater than 2 cm can be used if desired. For example, if thepulse 14 has a period of 0.2 nanoseconds (ns) (i.e., 2×10-10 sec), thenthe blind range is ½×2×10-10 s×3×1010 cm/s=3 cm. That is, for a target16 at a range of 3 cm from RADAR antenna 12, a 0.2 ns pulse wouldcomplete at exactly the time the reflection from beginning of the pulse14 is returned to the RADAR antenna 12 as the reflected signal 18. TheRADAR apparatus 12, 20, 22, 24 of the present disclosure detects the TOFor distance, d, of the object 16 through the full thickness of theportion of the patient support apparatus 10 through which pulse 14 andreflected signal 18 travel. Mattresses or pads used on patient supportsystems 10 are sometimes on the order of about 12 inches thick or more,for example.

The blind range is a term referring to the inability of the RADARantenna to adequately receive a reflected signal 18 during transmissionof the pulse 14. A pulse having a period of 6.25×10-11 seconds per pulsehas a blind range of 1.875 cm. Thus, to detect an object 16 at a rangeof 1.875 cm or more, the pulse period should be no longer than6.25×10-11 seconds. In some embodiments, driver circuitry 20 isconfigured as an ultra-wideband N-bit digitally tunable pulse generatorthat produces pulses typically as narrow as 0.55 ns (550 ps). Whiledetecting immersion of the patient 16 to within about 2 cm to about 2.5cm of bottoming out is possible according to this disclosure, in someembodiments, immersion of a patient to within about 5 cm to about 7 cmof bottoming out is sufficient. In such embodiments, the pulse periodcan be longer than the pulse periods just mentioned. Other systems, forexample using a bi-static RADAR described in connection with FIG. 2below, allow detection of the reflected signal 18 during the blindperiod.

Referring now to FIG. 17, the blind range of the RADAR system ismodified, in some embodiments, by insertion of an impedance-matcheddelay line 21 between RADAR antenna 12 and impedance matching circuitry22. Thus, the delay line 21 is coupled to the antenna 12 and to theimpedance matching circuitry 22. FIG. 17 illustrates the relevantsub-portion of the patient support apparatus 10 from FIG. 1 to show thelocation of the delay line 21 in the RADAR system. Delays may beinserted at other locations to achieve that same effect. It should beappreciated that the other elements of the patient support apparatus 10,such as circuitry 20, 24, 26, etc. shown in FIG. 1 are also included inthe RADAR system of FIG. 17 having delay line 21 for each antenna 12.Thus, the description above of the components of FIGS. 1-16, as well asvariants thereof, is equally applicable to the RADAR system of FIG. 17having delay line 21 for each antenna 12.

The delay line 21 creates the same effect as additional range betweenthe respective antenna 12 and the target 16: it takes the pulsegenerated by driver circuitry 20 longer to reach the radar antenna 12and similarly reflected signal 18 takes longer to return to the receivercircuitry 20. To illustrate this concept, consider the situation inwhich driver circuitry 20 (or a transceiver) emits a 1 nanosecond pulse14, the start of that pulse will have travelled d=c×1 nanosecond=30 cmbefore the RADAR antenna 12 completes transmission of the pulse 14. Ifthe range, d, to the target 16 is 15 cm or less, then the reflectedsignal 18 will return to the RADAR antenna 12 while the antenna 12 isstill emitting the pulse 14.

Now consider the situation in which the antenna 12 is connected to theimpedance matching circuitry 22, and therefore to the transceiver 20, bya length of RF transmission line, e.g., printed circuit board (PCB)microstrip, coaxial cable, a waveguide, or other type of delay line 21known to those familiar in the art, that is 30 cm long. Assuming thatthe RF signal travels at the speed of light, c, in the transmissionline, the leading edge of the pulse 14 reaches the antenna 12 as thetrailing edge leaves the transmitter (e.g., RF driver portion) 20 afterhaving traveled through the impedance matching circuitry 22 and delayline 21. The reflected signal 18 also takes an additional nanosecond toreach the receiver (e.g., RF receiver portion) 20 after having traveledthrough the delay line 21 and impedance matching circuitry 22. For anobject 16 that is 3 cm away from the antenna 12, the pulse 18 reflects1.1 nanoseconds after being emitted. By subtracting the known 1nanosecond delay created by the length of the delay line 21, theprocessor circuitry 24 of the RADAR system determines that thereflection occurred 0.1 nanoseconds after the pulse 14 left the antenna12. Multiplying by the speed of light, c, results in the actual range,d, being calculated as 3 cm.

Referring once again to FIG. 1, processor circuitry 24 is coupled topatient support system control circuitry 26 in the illustrative example.In some embodiments, each of circuitry 24, 26 include a microprocessoror microcontroller along with associated memory, power circuitry,input/output circuitry, clock or oscillator, etc. The microcontroller ofcircuitry 24 executes instructions to control the other portions ofRADAR apparatus 12, 20, 22 and circuitry 26 executes instructions tocontrol functions of patient support system 10. In other embodiments,circuitry 24 is included in circuitry 26. In such embodiments, amicroprocessor or microcontroller of circuitry 26 executes instructionsto control functions of the patient support system 10 and the RADARapparatus 12, 20, 22. In such embodiments, circuitry 26 is considered tobe the processor circuitry of the RADAR apparatus and the controlcircuitry of patient support system 10. Thus, the discussion above ofvarious processing and calculations made by circuitry 20, 24, such asthat regarding TOF and distance, d, determinations and regarding settingor adjusting bladder pressures, is performed by circuitry 26 in whole orin part, in some embodiments.

Circuitry 26 is coupled to a pneumatic system 28 of patient supportsystem 10 as shown diagrammatically in FIG. 1. Pneumatic system 28operates to control inflation of one or more air bladders 30 of patientsupport system 10. For example, if distance d or TOF is greater than afirst threshold distance or TOF, respectively, then the pneumatic system28 controls inflation by deflating one or more air bladders 30 so thatthe patient 16 immerses into the associated mattress or pad by a greaterextent, thereby, reducing the distance d or TOF and lowering interfacepressure between the patient 16 and the mattress or pad due to a greatersurface area of contact between the patient 16 and the mattress or pad.If distance d or TOF is less than a second threshold distance or TOF,respectively, then the pneumatic system 28 controls inflation byinflating one or more air bladders 30 so that the risk of the patient 16bottoming out is reduced due to increasing the distance d or TOF. Thus,in some embodiments, the pneumatic system 28 is operated by controlcircuitry 26 so that an amount of immersion of the patient 16 into apatient support surface is between the first threshold distance or TOFand the second threshold distance or TOF.

Pneumatic system 28 is shown diagrammatically in FIG. 1 and is intendedto represent the various components that are used to inflate and deflateair bladders 30. Thus, pneumatic system 28 includes one or more airsources such as a blower, compressor, or pump; one or more valves suchas solenoid valves, rotary valves, check valves, pressure relief valves;manifolds, manifold blocks; conduits such as tubes, hoses, passageways;pressure sensors; and the like.

Circuitry 26 is also coupled to one or more actuators 32 that areoperable to move movable components 34 of patient support system 10. Insome embodiments, actuators 32 include electromechanical actuators suchas linear actuators, motorized jack screws, motors that operate linkagesystems, and the like. In other embodiments, actuators 32 includehydraulic or pneumatic cylinders. Movable components 34 include sectionsof a mattress support deck in some embodiments. Such mattress supportdeck sections may include one or more of head, seat, thigh, and footsections. Other movable components include table tops of imaging tables,surgical tables, examination table, or the like; chair frame sections,wheelchair frame sections; patient lift sections; and the like.

In the case of a patient bed having a head section of a mattress supportdeck that pivotably raises and lowers relative to a seat section, anamount of weight of a patient bearing downwardly in a seat region of amattress supported by the seat section increase as the head section israised. Thus, according to this disclosure, if the TOF or distance, d,reaches a lower threshold limit indicative of a risk that the patientmay bottom out in the seat region of the mattress, the head section ofthe patient bed may be lowered automatically by control circuitry 26 orthe raising movement of the head section may be suspended by controlcircuitry 26. In some embodiments, the head section may resume raisingafter the pneumatic system has had time to inflate one or more bladders30 in the seat region of the mattress by a sufficient amount toeliminate the risk of the patient bottoming out if the head section wereto be raised further. A message during the suspension in raising thehead section may be displayed on a display screen of the patient bed insome embodiments to inform the user (e.g., a caregiver or patientpressing a head up button) that raising the head section is being pauseduntil the seat section is further inflated to prevent bottoming out ofthe patient.

Still referring to FIG. 1, patient support system 10 includes a powerinterface 35 and a network interface 36 coupled to control circuitry 26.Power interface 35 is configured to couple with a connector 37 at oneend of a power cord 39. An opposite end of the power cord 39 has astandard alternating current (AC) power plug 41 for connection to astandard AC power outlet. Network interface 36 includes, for example, aport for wired connection to a network 38 of healthcare facility and/ora transceiver for wireless communication with the network 38 via awireless access point in some embodiments. Data from RADAR apparatus 12,20, 22, 24 of patient support apparatus 10 is transmitted to at leastone remote server 40 for storage and analysis. Server 40 may be a nursecall server of a nurse call system such as the HILL-ROM® NAVICARE® nursecall system, an electronic medical records (EMR) server of an EMRsystem, or some other server such as the WELCH ALLYN® CONNEX® server.

If the TOF or distance d indicates that the patient 16 is at risk ofbottoming out, an alert message is transmitted from server 40 vianetwork 38 to a caregiver or clinician notification device 42. Examplesof clinician notification devices 42 according to this disclosureinclude handheld wireless communication devices such as smart phones,tablet computers, telephone handsets such as those available from ASCOMor Spectralink, for example, communication badges such as thoseavailable from Vocera, and pagers. Other types of clinician notificationdevices 42 include graphical audio stations that are mounted in patientrooms as part of a nurse call system and computer terminals that may beco-located with the clinician. Thus, one of servers 40 may be includedin a real time locating system (RTLS) that tracks the locations ofclinicians within a healthcare facility. The alert message is sent tothe notification device 42 that is at the same location as the clinicianassigned to the patient 16 who is at risk of bottoming out. The dataregarding TOF and/or distance, d, may be stored in server 40 at periodicintervals (e.g., every 5 minutes, every 15 minutes, every hour) so thata patient's immersion history profile may be generated by server 40 andso that compliance reports can be generated by server 40 relating towhether or not the patient bottomed out on a mattress of the patientsupport system 10.

In some embodiments, server 40 stores demographic data relating topatients 16 that are supported on various patient support systems 10.Thus, server 40 aggregates the data received by the control circuitry 26from the at least one RADAR system 12, 20, 22, 24 of various patientsupports systems 10 and transmitted by the respective control circuitry26 along with position data relating to the position of one or moremovable components 34 of the respective patient support system 10. Otherdemographic data concerning each patient is received by server 40 fromother sources, such as another server 40 such as anadmission/discharge/transfer (ADT) server 40, in some embodiments.Bedsore data including data relating to clinical results of bedsores isalso provided to server 40 for the various patients 16 on patientsupport systems 10. The demographic data relates to patient demographicsand includes, for example, patient condition such as being of limitedmobility, patient disease history, patient height, patient weight, andpatient age. Older patients have thinner skin and less mobility thanyounger patients, for example.

According to this disclosure, data mining of the information stored inserver 40 may be performed to discover correlations between the storeddata (e.g., demographic data, bedsore data, TOF data, distance d data,etc.). Thus, factors leading to better patient outcomes (e.g., lessbedsores) may be identified. For example, for a given mattressconfiguration, optimum ranges of patient immersion toward bottoming outmay be identified. The optimum ranges are the ranges of TOF and/ordistance, d, that result in the least amount of bedsore formation forpatients, for example. These optimum ranges may vary by patient size,weight, and age and may vary from mattress to mattress.

Referring now to FIG. 2, an alternative embodiment of a RADAR apparatusincludes a RADAR transmit antenna 12 a and a RADAR receive antenna 12 bthat is separate from the RADAR transmit antenna 12 a. Impedancematching circuitry 22 is coupled to the RADAR transmit and receiveantennae 12 a, 12 b. The alternative RADAR system has RF drivercircuitry 20 a that is separate from receiver circuitry 20 b. However,circuitry 20 a and circuitry 20 b are both coupled to the impedancematching circuitry 22. Furthermore, processor circuitry 24 is coupled tothe RF driver circuitry 20 a and receiver circuitry 20 b. In someembodiments, the RF driver circuitry 20 a, receiver circuitry 20 b, andthe processor circuitry 24 are packaged as an integrated circuit 44 asshown diagrammatically in FIG. 2 (in phantom). It should be understoodthat the one or more of the alternative RADAR apparatus 12 a, 12 b, 20a, 20 b, 22, 24 of FIG. 2 can be substituted for one or more of theRADAR apparatus 12, 20, 22, 24 of the patient support system 10 ofFIG. 1. Thus, the discussion above regarding FIG. 1 is equallyapplicable to RADAR apparatus 12 a, 12 b, 20 a, 20 b, 22, 24 of FIG. 2except where noted below.

In FIG. 1, pulse 14 and reflected signal 18 are illustrateddiagrammatically to be at an angle to each other for purposes ofdiscussion and for ease of illustration. However, when a single antenna12 is used as both the transmit antenna and the receive antenna (andconsidering the primary path), the transmitted pulse and reflectedsignal travel along basically the same path, such as vertically, in theillustrative arrangement of FIG. 1. However, in the FIG. 2 embodiment,the spacing between transmit antenna 12 a and receive antenna 12 bresults in an angular path for pulse 14 from antenna 12 a to the object16 and then for reflected signal 18 from the object 16 to receiveantenna 12 b. In order to calculate distance, d, in the FIG. 2arrangement, the angle of pulse 14 and/or reflected signal 18 should beaccounted for to obtain an accurate measurement. This can beaccomplished either by using angle α between the direction of pulse 14and horizontal (really, the plane of antenna 12 a, 12 b which isillustratively horizontal) or by using angle β between the direction ofreflected signal 18 and vertical (really, the direction normal to theplane of antenna 12 a, 12 b which is illustratively vertical). Thedistance, d, can be calculated as either d=(TOF×c/2)×sine(α) ord=(TOF×c/2)×cosine(β).

Once distance, d, is determined, it can be used as the control parameterby control circuitry 26 for adjusting inflation of bladders 30 and/ormoving one or more movable components 34 of the patient support system10 in the same manner as described above. It should also be noted thatTOF can still be used as the control parameter with regard to adjustinginflation of bladders 30 and/or moving movable components 34 of patientsupport system 10 in the RADAR apparatus embodiment of FIG. 2 as long asthe appropriate minimum and maximum TOF thresholds are selectedcorresponding to the minimum desired distance, d, toward bottoming outand the maximum distance, d, for desired interface pressure distributionof the patient 16 on the mattress or pad.

Referring now to FIG. 3, another alternative embodiment of a RADARapparatus includes a multiplexer 46 to connect RF driver/receivercircuitry 20 and processor circuitry 24 to selected ones of radarantennae 12 via corresponding impedance matching circuitry 22. Thus,unlike the RADAR apparatus embodiment of FIG. 1 in which each antenna 12has its own circuitry 20, 24, the RADAR apparatus embodiment of FIG. 3uses multiplexer 46 so that circuitry 20, 24 is shared among the RADARantennae 12. Accordingly, the RADAR apparatus 12, 20, 22, 24, 46 of FIG.3 is less costly and has less circuit components than the embodiment ofFIG. 1.

Multiplexer 46 may be operated in any desired manner to cycle throughthe RADAR antennae 12 to select which one of RADAR antenna 12 is activefor emission of pulse 14 and receipt of reflected signal 18 with theremaining antennae 12 being dormant. In further variants, each antenna12 of the FIG. 3 embodiment is replaced with antennae 12 a, 12 b of FIG.2 and/or circuitry 20 of the FIG. 3 is replaced with circuitry 20 a, 20b of FIG. 2. It should be understood that the alternative RADARapparatus 12, 20, 22, 24, 46 of FIG. 3, or its variants just mentioned,can be substituted for the RADAR apparatus 12, 20, 22, 24 of the patientsupport system 10 of FIG. 1. Thus, the discussion above regardingcontrol of the patient support system 10 by circuitry 26 based ondistance, d, or TOF in connection with FIG. 1 is equally applicable toRADAR apparatus 12, 20, 22, 24, 46 of FIG. 3 and its variants.

RADAR apparatus 12, 20, 22, 24 receives the power for operation fromcontrol circuitry 26 of patient support apparatus 10 in someembodiments. Circuitry 26 receives its power from power cord 39 thatplugs into an AC power outlet in room of a healthcare facility, forexample. Power interface 35 and/or circuitry 26 includes power isolationcircuitry and power conversion circuitry to convert the 110-250 Volt,50/60 Hertz standard AC power into the various voltage levels (e.g., 5 VDC, 24 V DC, 12 V DC) required to operate the various components of thepatient support apparatus 10, including the RADAR apparatus 12, 20, 22,24. In some embodiments, power interface 35 and/or control circuitry 26includes one or more batteries that provide power to the variouscomponents of patient support apparatus 10, including the RADARapparatus 12, 20, 22, 24 when the power cord 39 is unplugged from the ACpower outlet. Other RADAR architectures known to those familiar with theart may be used.

In some embodiments it is contemplated that each antenna 12 is a planarantenna. Having a planar or flat antenna 12 permits use of the antenna12 inside of a mattress or pad, as will be discussed below in connectionwith FIGS. 10A-10C, or just underneath a mattress or pad, as will bediscussed below in connection with FIGS. 11A and 11B, without resultingin a large bump or protrusion which would potentially be felt by thepatient 16 or interfere with the support capabilities of the mattress orpad. Examples of suitable planar antennae 12 are shown in FIGS. 4 and 5.

Referring to FIG. 4, an Archimedean spiral antenna 12′ is shown.Archimedean spiral antenna 12′ may be used as any of antennae 12, 12 a,12 b discussed above in connection with FIGS. 1-3. Antenna 12′ includesa conductive first arm 48 that electrically couples to a positiveterminal of a voltage feed 52 and a conductive second arm 50 thatelectrically couples to a negative terminal of the voltage feed 52.Voltage feed 52 is the interface between impedance matching circuitry 22and antenna 12′. The geometry of arms 48, 50 is the same, although thearms 48, 50 are rotated 180 degrees with respect to each other, and isdefined by the formula, r=a φ in which r is the radius from the centerof the spiral, a is coefficient and φ is the angle from the startingpoint of the spiral. In the illustrative example, a=0.1. Also in theillustrative example, a short, straight, conductive segment 54interconnects an inner end of each arm 48, 50 to the voltage feed 52.

Referring to FIG. 5, a log-periodic spiral antenna 12″ is shown.Log-periodic spiral antenna 12″ may be used as any of antennae 12, 12 a,12 b discussed above in connection with FIGS. 1-3. Antenna 12″ includesa first conductive arm 56 that electrically couples to the positiveterminal of voltage feed 52 and a conductive second arm 58 thatelectrically couples to the negative terminal of the voltage feed 52.Voltage feed 52 is the interface between impedance matching circuitry 22and antenna 12″. The geometry of arms 56, 58 is the same, although thearms 56, 58 are rotated 180 degrees with respect to each other, and isdefined by the formula, r=Roe aφ in which r is the radius from thecenter of the spiral, Ro is a constant that dictates the initial radiusof the spiral, a is coefficient that dictates the amount that each arm56, 58 flares or grows as it turns, and φ is the angle from the startingpoint of the spiral. A suitable value for a is 0.22. In the illustrativeexample, short, straight, conductive segments 54 interconnect inner endsof each arm 46, 58 to the voltage feed 52.

The antenna beam from antenna 12′, 12″ is normal to the plane of theantenna 12′, 12″. Furthermore, the number of turns of arms 48, 50 ofantenna 12′ and the number turns of arms 56, 58 of antenna 12″ may rangefrom about ½ turn to about 3 turns at the option of the designer, withabout 1½ turns being a typical number for spiral antennae. Spiralantennae 12′, 12″ also have the benefit of exhibiting the antennacharacteristic of circular polarization. Circular polarization is oftenused because it has a good ability to reject specular reflectioncomponents of multipath signals. Specular reflections in RADAR systems,such as those off of metallic surfaces, will have a circularpolarization that is in the opposite polarity (rotating the oppositedirection) compared to the incident signal (e.g., pulse 14) whereas thereflected signal 18 of interest will have the same polarity. Thus, byuse of circular polarization, the signals with the opposite rotationdirection from the pulse 14 are rejected by the antenna. That is, aright-hand (RH) circularly-polarized antenna cannot receive left-hand(LH) circularly polarized signals because reflections of a RH circularlypolarized signal from a metal surface would be LH circularly polarizedand rejected. Thus, by using spiral antennae 12′, 12″ the reflectedsignal 18 of interest is accepted with less noise from specularreflections of opposite polarity. Spiral antennae also have a largebandwidth and are suitable for operating over a wide range offrequencies as are required for ultra-wide band (UWB) RADAR systems.

Voltage feed 52 of impedance matching circuitry 22 of the presentdisclosure is configured as a balun in some embodiments. Thus, thevoltage feed 52 is sometimes referred to herein as balun 52. A balun isa type of transformer that is used to convert an unbalanced signal to abalanced one or vice versa. Baluns isolate a transmission line andprovide a balanced output. The term is derived by combining the wordsbalanced and unbalanced. Use of a balun 52 with the antennae disclosedherein ensures that both arms of the spiral antenna (e.g., arms 48, 50of antenna 12′ and arms 56, 58 of antenna 12″) have balanced currents. Abroadband balun 52 should be use for a wide-band antenna.

Referring now to FIG. 6, balun 52 is configured as an infinite balun,which in the illustrative example, includes a coaxial cable that iselectrically coupled to spiral antenna 12′. The coaxial cable has itscenter conductor 60 coupled to first arm 48 of antenna 12′ and has itsouter conductor or ground shielding coupled to second arm 50 of antenna12′. Outer cladding 62 of the coaxial cable surrounds the groundshielding and thus, the ground shielding cannot be seen in FIG. 6.However, coaxial cables have well-known structures.

Referring now to FIG. 7, a second embodiment of an infinite balun isshown. In the second embodiment, a coaxial cable 64 extends from a radio66 (e.g., RF driver/receiver circuitry 20 of FIG. 1) and is spiraled toform a first arm of a spiral antenna 12′″. In particular, the outerconductor or ground shielding of coaxial cable 64 is used as the firstarm of antenna 12′″. Antenna 12′″ includes a conductive second arm 68 aswell. Antenna 12′″ may be used as any of antennae 12, 12 a, 12 bdiscussed above in connection with FIGS. 1-3. The coaxial cable 64 ofthe spiral antenna 12′″ serves as a portion of the RADAR antenna 12′″and as a portion of the impedance matching circuitry 22. Thus, coaxialcable 64 and balun 52 and one of the conductive arms of antenna 12′″ areone in the same in the embodiment of FIG. 7.

Optionally, a tapered balun rather than an infinite balun 52 may be usedin impedance matching circuitry 22 as a voltage feed to the antennae 12,12 a, 12 b, 12′, 12″, 12′″ disclosed herein. A tapered balun graduallychanges shape from an unbalanced transmission line to a balancedtransmission line. One type of tapered balun 52′ is shown in FIG. 8 andanother type of tapered balun 52″ is shown in FIG. 9. In FIG. 8, aportion of a coaxial cable 70 has its outer conductor 72 provided with aV-shaped notch 74 to permit the outer conductor 74 to be peeled awayfrom a center conductor 76 so that an end region of the peeled awaymaterial can be reshaped into a conductor 78 having a shape that issubstantially the same as the center conductor 76. Conductors 76, 78 aretransmission lines having substantially equivalent shapes at the end ofcoaxial cable 70 and these transmission lines 76, 78 provide thepositive and negative terminals for electrically coupling to theassociated antenna such as antenna 12′. The geometry of the taper formedby notch 74 should be gradual so as to extend over several wavelengthsof the expected pulse 14.

Referring now to FIG. 9, tapered balun 52″ is formed in a microstriptransmission line 80. Transmission line 80 has a top strip 82 of uniformwidth between its opposite elongated edges 84. Transmission line 80 alsohas a bottom strip 86 which serves as a ground plane and which has awide portion defined between its elongated opposite edges 88. Strip 86tapers down to an end portion 90 having a substantially equivalent widthbetween edges 92 as the width of top strip 82 between edges 84. Strip 86has tapered edges 94 that transition from respective edges 88 tocorresponding edges 92. Thus, end portion 90 of strip 86 hassubstantially the same shape as the overlying portion of strip 82.Accordingly, a balanced transmission line is provided at the end portionof the tapered balun 52″. The taper of edges 94 should be gradual so asto extend over several wavelengths of the expected pulse 14. Strip 82serves the positive terminal and provides the RF feed to one of the armsof the associated antenna, such as antenna 12′, and strip 86 serves asthe negative terminal which couples to the other arm of the associatedantenna.

In the discussion of FIGS. 10A-16 that follows, reference is made simplyto antenna 12 or antennae 12. However, each antenna embodiment disclosedherein (e.g., antenna 12, 12 a, 12 b, 12′, 12″, 12′″) is contemplated asbeing a suitable antenna for use in the structures shown in FIGS.10A-16. Also, the discussion that follows refers to various types of“mattresses.” However, the discussion is equally applicable to mattressoverlays, surgical pads, chair cushions or pads, and the like.

Referring now to FIG. 10A, a cross sectional view of a portion of an airmattress or support pad 100 a is shown. Air mattress 100 a supports thepatient 16 thereon and includes a plurality of air bladders 30. Inparticular, with regard to the portion of mattress 100 a shown in FIG.10A, portions of air bladders 30 a, 30 b, 30 c can be seen. Bladders 30a, 30 b, 30 c each include a layer of flexible material 31 that issubstantially air impermeable and configured to form an enclosure tocontain a volume of pressurized air therein. Mattress 100 a includes abase foam layer 102 underlying bladders 30 a-c. Mattress 100 a alsoincludes an outer ticking 104 including a top ticking layer 106 and abottom ticking layer 108. Mattress 100 a is supported by a frame 110 ofpatient support system 10. Mattress also includes a fire sock (notshown) which surrounds base foam layer 102, bladders 30 a-c, any otherbladders 30 of mattress 100 a, and any other components of mattress 100a inside of the ticking 104, as is well known in the art. The patientsupport elements or components inside of the ticking 104 of mattress 100a, such as bladders 30 a-c and base foam layer 102 in the FIG. 10Aexample, are considered to be the core of mattress 100 a.

In the embodiment of FIG. 10A, RADAR antenna 12 is located inside ofmattress 100 a and is sandwiched between bottom ticking layer 108 andbase foam layer 102. In the illustrative example, base foam layer 102conforms around RADAR antenna 12. It should be appreciated thatadditional RADAR antennae 12 are sandwiched between bottom ticking layer108 and base foam layer 102 at other locations throughout mattress 100 ain some embodiments. The locations of RADAR antenna 12 within mattress100 a is at the discretion of the mattress designer. Each antenna 12 isoperated to emit pulse 14 and receive reflected signal 18 as has beendescribed above to determine TOF and, in some embodiments, distance dwhich is dictated by an amount of immersion of the patient 16 intomattress 100 a in the region above antenna 12. It should be appreciatedthat conductors of the antenna feed 52 (or antenna feed 52′, 52″ as thecase may be) are routed, at least in part, within the interior region ofthe mattress 100 a.

Optionally, in some embodiments, a RADAR reflective coating 112 isprovided on an inner surface of the top portion of material 31 ofbladder 30 a. In such embodiments, the RADAR reflective coating becomesthe target or object which reflects pulse 14 as the reflected signal 18and therefore, it is the TOF and/or distance, d, between RADAR antenna12 and the RADAR reflective coating 112 which is determined orcalculated. However, using the reflective coating 112 as the object ortarget still permits a determination to be made regarding the patient'srisk of bottom out so that corrective action can be taken by circuitry26 of patient support system 10 to mitigate the risk as discussed above.

Referring now to FIG. 10B, a cross sectional view of a portion of an airmattress or support pad 100 b similar to the one of FIG. 10A is shown.Thus, the same reference numbers are used in FIGS. 10A and 10B to denotelike components. Furthermore, the description of above of the componentsof mattress 100 a of FIG. 10A is equally applicable to the likecomponents of mattress 100 b of FIG. 10B. The primary difference betweenmattress 100 a and mattress 100 b is that base foam layer 102 is omittedin mattress 100 b. Also, in the mattress 100 b of FIG. 10B, the lowerportion of material 31 of bladder 30 a conforms around antenna 12 whichis sandwiched between the bottom ticking layer 108 and the lower portionof material 31 of bladder 30 a.

Many mattresses have a base foam layer like layer 102 of mattress 100 aof FIG. 10A to provide some cushioning for the patient 16 in the eventof a bottoming out situation (e.g., the top portion of material 31 ofbladder 30 a is deflected all the way down under the weight of patient16 to contact the bottom portion of material 31 of bladder 30 a).However, because RADAR antenna 12 and the associate circuitry 20, 22, 24of the RADAR apparatus provides an output to control circuitry 26 of thepatient support apparatus 10 which, in appropriate circumstances,signals pneumatic system 28 to further inflate one or more bladders 30and/or to signal one or more actuators 32 to move one or more associatedmovable components 34 so as to prevent the bottoming out condition, itis possible to eliminate base foam layer 102 from mattress 100 a asshown in the mattress 100 b embodiment of FIG. 10B.

Because base foam layer 102 is eliminated in mattress 100 b of FIG. 10B,mattress thickness in the vertical dimension is less than the mattress100 a of FIG. 10A which has base foam layer 102. In other words, thethickness of mattress 100 b is reduced by the amount of thickness ofbase foam layer 102 of mattress 100 a which can be on the order of about1 inch to about 3 inches or more in some mattresses. Having a “thinner”mattress 100 b as compared to mattress 100 a results in other designadvantages to the frame 110 of patient support system 10. For example,in the embodiments in which patient support system 10 is a patient bedhaving frame 110 equipped with one or more siderails that each movebetween a raised position to block patient egress from the mattress 100b and a lowered position to permit patient egress, a vertical height ofthe one or more siderails of the patient bed 10 does not need to be aslarge with a thinner mattress. When such reduced height siderails are inthe lowered positions, an upper frame portion of frame 110 can belowered relative to a base frame portion of frame 110 (or relative tothe underlying floor) to a lowermost position, sometimes referred to asa low/low position in the art, that places the patient 16 closer to thefloor as compared to beds 10 having mattresses 100 a with base foamlayers 102 while still maintaining a sufficient gap between a bottom ofthe siderail and the floor to meet governmental and hospitalregulations.

Referring now to FIG. 10C, a cross sectional view of another embodimentof a mattress or pad 100 c is shown. Portions of mattress 100 c that aresubstantially the same as like portions of mattress 100 a are denoted bylike reference numbers and the description above is equally applicable.Thus, the illustrative RADAR antenna 12 in FIG. 10C is sandwichedbetween the bottom ticking layer 108 and base foam layer 102 whichconforms around RADAR antenna 12. One of the noticeable differencesbetween mattress 100 c of FIG. 10C and mattress 100 a of FIG. 10A isthat instead of the single layer of bladders 30, including illustrativebladders 30 a-c of mattress 100 a, mattress 100 c has multiple layers ofbladders 30. In particular, mattress 100 c has a lower layer of bladders30 above base foam layer 102 and an upper layer of bladders 30 above thelower layer of bladders. In FIG. 10C, portions of bladders 30 d, 30 e,30 f can be seen in the lower layer and portions of bladders 30 g, 30 h,30 i, 30 j, 30 k can be in the upper layer. Mattress 100 c is configuredso that three bladders 30 of the upper layer are situated above eachbladder 30 of the lower layer. For example, bladders 30 g, 30 h, 30 i ofthe upper air bladder layer of mattress 100 c are situated over bladder30 d of the lower air bladder layer of mattress 100 c.

Another difference between mattress 100 a of FIG. 10A and mattress 100 cof FIG. 10C is that mattress 100 c has a microclimate management (MCM)layer 114 above the upper layer of bladders 30, such as bladder 30 g-k,portions of which can be seen in FIG. 10C. In the illustrative example,upper ticking layer 106 is included as one of the components of MCMlayer 114. MCM layer 114 also includes a bottom sheet or layer 116 and athree-dimensional (3D) engineered material layer 118 situated betweenlayers 106, 116. The 3D engineered material 118 comprises an airpermeable material which allows a stream of air to flow therethrough towick moisture away from the patient 16 through upper ticking layer 106.Examples of suitable 3D engineered material includes, but is not limitedto, fiber networks made from textile fabrics such as is shown anddescribed in U.S. Pat. Nos. 5,731,062 and 5,454,142 owned by HoechstCelanese Corporation, Somerville, N.J. and marketed as SPACENET®material. Other examples of suitable 3D engineered material includesModel No. 5875, 5886, 5898, and 5882 materials available from MullerTextile of Troy, Mich. and a molded thermoplastic spacer matrix materialavailable from Akzo Nobel of Amsterdam, Netherlands. Thus, the term“three-dimensional (3D) engineered material” is meant to include any ofthese types of materials and similar materials.

RADAR antenna 12 of mattress 100 c shown in FIG. 10C emits pulse 14 andreceives reflected signal 18 through all of the illustrative componentsof mattress 100 c that are situated between RADAR antenna 12 and thepatient 16. Thus, the pulse 14 and reflected signal travel through foambase layer 102, one or more of bladders 30 d-f of the lower bladderlayer, one or more of bladders 30 g-k of the upper bladder layer, MCMlayer 114, and any other components of mattress 100 c (e.g., a firesock) included in mattress 100 c and situated between RADAR antenna 12and the patient 16.

As should be apparent from the mattress examples shown in FIGS. 10A-10C,RADAR apparatus 12, 20, 22, 24 can be used with mattresses or pads ofall types regardless of the simplicity or complexity of the mattressdesign. In the examples of mattresses 100 a-c of FIGS. 10A-10C, one ormore RADAR antenna 12 are located inside of the respective mattress 100a-c. While RADAR antennae 12 are placed just above bottom ticking layer108 in the illustrative examples of mattresses 100 a-c, it is within thescope of this disclosure for RADAR antennae 12 to be placed elsewherewithin the respective mattress 100 a-c, such as on top of base foamlayer 102 or inside of one or more of the bladders 30. However, it ispreferable to place the RADAR antennae 12 close to the bottom of themattress 100 a-c, in the manner illustrated, so that the blind range ofthe RADAR apparatus 12, 20, 22, 24 is as close to the bottom of themattress 100 a-c as possible. RADAR antenna 12 may be secured in placewithin mattress 100 a-c with adhesive, adhesive tape, hook-and-loopfasteners such as VELCRO® material, and the like. In some embodiments,additional material may be attached to an inner surface of bottom layerof ticking 108, such as by RF or sonic welding or by stitching, forexample, to provide pockets which receive RADAR antennae 12.

Referring now to FIG. 11A, a mattress 100 is exploded away from and anarticulated mattress support deck 120 of frame 110 of the patientsupport apparatus 10. Deck 120 is illustrated in a simplified manner inFIG. 11A but is generally representative of those used on patient beds,stretchers, and surgical tables. Deck 120 includes a head or backsection 122, a seat section 124, a thigh section 126, and a foot section128. Head section 122 is pivotably coupled to a head end of seat section124 and thigh section 126 is pivotably coupled to a foot end of seatsection 124. Foot section 128 is pivotably coupled to a foot end ofthigh section 126. In some patient beds, seat section 124 is affixed toan upper frame with sections 122, 126, 128 being movable, such as withthe use of actuators 32, relative to seat section 124. Thus, sections122, 126, 128 are articulated to various positions to support themattress 100, and therefore, the patient 16 supported by mattress 100,in various positions.

Each of illustrative sections 122, 124, 126, 128 includes a framework130, typically made of a metal material such as steel, and a supportpanel 132 that is situated atop the respective framework 130. Supportpanels are made of radiolucent materials such as a molded plasticmaterial or carbon fiber or fiberglass or the like, although, it iswithin the scope of this disclosure for panels 132 to be made from ametal material if desired. Each panel 132 has an upper surface 134. Inthe illustrative example, RADAR antennae 12 a, 12 b, 12 c, 12 d, 12 e,12 f, 12 g are coupled to upper surfaces 134 of panels 132.Specifically, RADAR antennae 12 a, 12 b are coupled to upper surface 134of panel 132 of head section 122; RADAR antennae 12 c, 12 d, 12 e arecoupled to upper surface 134 of panel 132 of seat section 124; and RADARantennae 12 f, 12 g are coupled to upper surface 134 of panel 132 offoot section 128.

The location of RADAR antennae 12 a-g on deck 120 generally coincidewith locations at which bony prominences of the patient 16 would beexpected when the patient 16 is lying in a supine position on mattress100. Thus, RADAR antennae 12 a, 12 b are situated on head section 122beneath the general locations where the right and left scapula of thepatient 16 would be expected to lie on mattress 100. RADAR antennae 12c, 12 d, 12 e are situated on seat section 124 beneath the pelvic orsacral region of the patient 16. In particular, RADAR antennae 12 c, 12e are situated on seat section 124 beneath the general locations wherethe patient's right and left iliac tuberosity would be expected to lieon mattress 100 and RADAR antennae 12 d is situated on seat section 124beneath the general location where the patient's coccyx would beexpected to lie on mattress 100. Finally, RADAR antennae 12 f, 12 g aresituated on foot section 128 beneath the general locations where thepatient's right and left heels would be expected to lie on mattress 100.

It is within the scope of this disclosure to provide more RADAR antennae12 on deck 120 than is shown in FIG. 11A. For example, in someembodiments, an additional RADAR antenna 12 is provided on head section122 beneath the patient's head, but typically a pillow is placed underthe patient's head and provides additional cushioning such that pressureulcers are less likely on the patient's head than in the region of thepatient's scapulae. One or more RADAR antennae 12 may be included onthigh section 126 as well, although, the thighs of patients typicallyare not susceptible to pressure ulcers. It is also within the scope ofthis disclosure to provide less RADAR antennae on deck 120 than is shownin FIG. 11A. For example, RADAR antennae 12 d may be omitted in someembodiments. It should be appreciated that a respective antenna feed 52is routed to each of RADAR antennae 12 a-g, such as extending upwardlythrough respective holes (not shown) provided in panels 132 beneathantennae 12 a-g or by being routed along upper surfaces 134 of panels132 to the respective antennae 12 a-g.

In some embodiments, RADAR antennae 12 a-g protrude upwardly by a slightamount from upper surfaces 134 of panels 132 (e.g., see FIG. 11B). Inother embodiments, panels 132 of deck 120 are provided with recesses orpockets in which RADAR antennae 12 a-g are situated so that uppersurfaces of the antennae 12 a-g, or housings that may contain antennae12 a-g, are substantially flush or coplanar with surfaces 134 of panels132. The present disclosure contemplates various types of fasteners thatmay be used to couple RADAR antennae 12 a-g to deck 120. For example,adhesive such as glue or adhesive tape may be used in some embodiments.Hook-and-loop fasteners such as VELCRO® material may be used in someembodiments. In embodiments in which RADAR antennae 12 a-g includehousings, screws may be used to attach antennae 12 a-g to panels 132 ofdeck 120. Snaps and clips are other examples of a suitable fastener forcoupling RADAR antennae 12 a-g to deck 120.

By providing RADAR antennae 12 a-g on deck 120, rather than inside ofmattress 100, the RADAR apparatus 12, 20, 22, 24 of the associatedpatient support system 10 may be used with any type of mattress placedon deck 120 to determine whether the patient is at risk of bottoming outon the particular mattress. In some embodiments, the patient supportsystem 10 includes a user interface, such as a graphical user interface(GUI), which is used to select the type of mattress being supported ondeck 120. For example, the GUI of system 10 may be used to indicate thatone of mattresses 100 a-c described above is the particular type ofmattress supported on deck 120. Control circuitry 26 then may sendinformation to processor circuitry 24 indicating the type of mattress ondeck 120.

Different types of mattresses will have different impedances dependingupon their particular constructions. According to this disclosure, theimpedance of impedance matching circuitry 22 is adjusted to match theenvironment through which pulse 14 and reflected signal 18 travel. Thus,circuitry 26 and/or circuitry 24 includes information regarding theimpedances of different mattress types and the impedance matchingcircuitry 22 is adjusted to match that of the particular mattress beingused on deck 120. In this regard, switches such as transistors ormicroswitches may be turned on and off to select respective impedanceelements (e.g., resistors, capacitors, inductors) for inclusion in theimpedance matching circuitry 22 or exclusion from the impedance matchingcircuitry 22.

Alternatively or additionally, an impedance element may be dynamicallyadjusted to change the impedance of circuitry 22. For example, a rotarypotentiometer or rheostat may be adjusted, such as with a small motor,to change its resistance. Similarly, an adjustable capacitor may havethe spacing between its plates adjusted or the surface area of overlapadjusted in the case of a rotary variable capacitor to change itscapacitance. A variable inductor in which a magnetic core is adjustedwithin a coil of wire to change its inductance is also contemplated.Furthermore, different zones of a mattress may have different impedancesdepending upon the construction of the various zones. Thus, impedancematching circuitry 22 for each RADAR antennae 12 a-g on deck 120 may bedifferent depending upon the construction of the portion of the mattresslocated above the particular RADAR antennae 12 a-g.

Referring now to FIG. 11B, a cross sectional view of a foam mattress 100d is shown. Foam mattress 100 d is filled with one or more foam layers136 within ticking 104 between upper ticking layer 106 and bottomticking layer 108. In the illustrative embodiment, one layer 136 of foamserves as the core of mattress 100 d but in other embodiments, two ormore layers of foam may be provided to serve as the core within ticking104. Also in the illustrative example of FIG. 11B, RADAR antenna 12 islocated on deck 120 of frame 110 of the patient support system 10beneath the bottom layer of ticking 108 which, together with a portionof foam layer 136, conforms around RADAR antenna 12.

Even though there are no air bladders in mattress 100 d to be adjusted,there is still a benefit in using RADAR apparatus 12, 20, 22, 24 tomonitor the immersion of the patient 16 into mattress 100 d bymonitoring or determining the TOF or the distance, d. Over time, thesupport characteristics of foam are known to degrade. Depending upon thetype of foam, mattress 100 d may get harder over time, due to oxidationfor example, or mattress 100 d may get softer, due to fracturing of thecellular material of the foam. Also, some foam materials, such asviscoelastic foam, may become permanently compressed or deformed,thereby losing its cushioning capabilities and becoming harder. Thus,depending upon the weight of the patient 16 as measured by weight scaleof the patient support system 10, the amount of immersion into mattress100 d may be expected to be between a maximum and minimum threshold.

The minimum immersion threshold corresponds to a maximum threshold forTOF and/or distance, d, and the maximum immersion thresholdcorresponding to a minimum TOF and/or distance, d. Some or all of thesemaximum and minimum thresholds may be stored in memory of circuitry 26or circuitry 24. If RADAR system 12, 20, 22, 24 used with a foammattress, such as mattress 100 d, indicates that TOF or distance, d, isgreater than the maximum threshold for the patient 16 of a given weight,then this is indicative that the foam layer 136 in mattress 100 d hasdegraded and become too hard. On the other hand, if RADAR system 12, 20,22, 24 used with a foam mattress, such as mattress 100 d, indicates thatTOF or distance, d, is smaller than the minimum threshold for thepatient 16 of a given weight, then this is indicative that the foamlayer 136 in mattress 100 d has degraded and become too soft. In eithercase, if the mattress has become too hard or too soft, an alert messageis provided, such as being communicated from circuitry 26 to one or moreclinician notification devices 42 via network 38, to indicate thatmattress 100 d should be replaced.

The present disclosure contemplates that a standalone RADAR apparatus12, 20, 22, 24 may be used with the patient support systems 10 disclosedherein, rather than been integrated into the particular patient supportsystem such as at the time of manufacture. Thus, a standalone RADARapparatus may retrofit onto an existing patient support system 10 suchas a patient bed. The RADAR antennae 12 may be placed beneath thecorresponding mattress and the other elements 20, 22, 24 may be packagedin a housing that attaches to the existing patient support system.Antennae 12 may be held in place with suitable fasteners (e.g., VELCRO®fasteners, straps, bands, screws, etc.) or adhesive or tape. Circuitry24 may couple to an input port of circuitry 26 of the patient supportsystem 10 for data exchange in some embodiments. Therefore, circuitry 24may provide the standalone RADAR apparatus 12, 20, 22, 24 withplug-and-play capability by downloading software to circuitry 26 whichcircuitry 26 uses to control the respective pneumatic system 28 and/oractuators 32, for example, based on the data (e.g., TOF and/or distancedata) received from circuitry 24.

A standalone RADAR apparatus 12, 20, 22, 24 also may be used forend-of-life testing of a mattress, particularly of a foam mattress likethat shown in FIG. 11B or a mattress having foam components. In such anembodiment, one or more RADAR antennae 12 is placed beneath the mattress100 d and one or more weights of known value may be placed atop themattress 100 d at one or more corresponding designated locations. If themattress 100 d has become too hard (e.g. d greater than a maximumthreshold) or too soft, (e.g. d less than a minimum threshold), asdescribed above in connection with FIG. 11B, an alert message isprovided, such as being displayed on a display screen provided with thehousing carrying RADAR apparatus elements 20, 22, 24, for example.

The “weight(s) of known value” referred to above can be inanimate testweights or can be patient weights, or ranges of patient weights. In theexample of FIG. 20 circular data symbols represent a first range ofpatient weights (light weight), square data symbols represent a secondrange of patient weights (intermediate weight), and triangular datasymbols represent a third range of patient weights (heavy weight). Thevertical axis is a measure of the life status, LS, of the mattress, forexample remaining life or expended life as determined from distance d ortime of flight TOF. Generally speaking, the mattress's lifetime toprovide therapeutic support is less for heavier patients. The horizontalaxis is a time stamp indicating when life status LS was determined.Different patients (PA through PG) occupy the mattress at differenttimes. A comparison of values of LS across different weight ranges mightmake difficult the estimation of the life status of the mattress withouta large number of samples. However as information is accumulated it maybe easier to estimate the life status for any given patient weightrange, as suggested by the dashed lines. By way of example, if the lifestatus LS is remaining life, the mattress under consideration may bejudged to have considerable life remaining if it is used for lighterweight patients, but may be near the end of its ability to adequatelysupport heavier patients.

The foregoing reference to “weights of known value” includes the limitcase of no weight at all. For example, FIGS. 21-22 show the case of lifestatus (represented by remaining life) determined by applying zero testweight to a mattress. At an early stage of the life of mattress,distance d from radar antenna 12 to the top surface of the mattress mayhave a value d1, yielding a time of flight TOF1 and an assessment thatthe remaining useful life of the mattress is RL1. After a period ofadditional use, distance d from radar antenna 12 to the top surface ofthe same mattress may have diminished to a value d2, for example due topermanent deformation of foam components resulting from repeated useover a lengthy period of time. The pulse from radar antenna 12 has atime of flight TOF2, which is less than TOF1. The assessment of theremaining useful life is RL2, which is less than RL1. The graph of FIG.22 shows the vertical distances of FIG. 21 (right side scale) and theremaining life of the mattress (left side scale). The graph if FIG. 22is illustrative; the actual relationships between life and time offlight and between distance and time of flight may be nonlinear.

In view of the foregoing, a patient support surface for supporting apatient includes a core including at least one patient support element,and a ticking surrounding the core. The ticking has an upper layeroverlying the core and a lower layer underlying the core. At least oneradio detection and ranging antenna is situated beneath the upper layer,for example beneath the core. The antenna emits a pulse that travelsthrough the core and that is reflected by either the patient or thediscontinuity from the mattress to air, or by an inner surface of theupper layer of the ticking as a reflected signal back to the at leastone radar antenna. The support surface also includes circuitry such asprocessor circuitry 24 that determines a time-of-flight (TOF) of thepulse and the reflected signal to determine the life status (e.g. theremaining life) of the patient support surface. The determination may bemade while a load bears on the support surface or when the supportsurface is unloaded. A load, if applied, may be an inanimate weight ormay be the weight of a patient. An unloaded support surface may beconsidered to be a limit case of a loaded surface in which the loadequals zero.

The foregoing describes way of determining life status that may bethought of as nondynamic (static or quasi-static) in the sense that thedetermination is based on a known constant weight being used atdifferent times and does not involve the consideration of short termtransient response of the mattress to the weight. However the lifestatus LS of a foam mattress or a mattress having foam components mayalso be determined dynamically by examining the deformation transient ofthe mattress in response to the application or removal of a test weight.The block diagram of FIG. 23 shows a sequence of actions for making thelife status assessment. At block 306 a nonzero weight W is applied tothe mattress at a time designated as t=0. The application of the weightopens a measurement window during which the time of flight of one ormore radar pulses is used at block 308 to establish how distance dchanges in response to the application of the weight. Block 310establishes whether or not the deformation transient is complete. Somediscretion may be applied in determining when the transient isconsidered to be complete. For example the transient may be judged to becomplete after a specified number of time constants or after d becomesless than a specified fraction of its original value or after its rateof change becomes less than a prescribed value. Once the deformationtransient is complete the measurement window closes and the methodbranches to block 312 where the life status is assessed as a function ofthe temporal profile of the deformation. Examples of parameters thatrepresent the life status of the mattress include estimated liferemaining and estimated life expended.

One method for carrying out the assessment at block 312 is illustratedin FIGS. 24-26. FIG. 24 shows an example of deformation (as revealed bydistance d) over time. The temporal profile of the deformation isillustrated as a decay having a time constant τ. The example graph ofFIG. 25 shows an illustrative relationship between remaining life of thefoam components of the support surface and τ in which higher values of τindicate longer remaining life. The example graph of FIG. 26 shows anillustrative relationship in which higher values of τ indicate shorterremaining life. The direction of the relationship between life and τ(FIG. 25 vs 26) may depend on factors such as the mechanisms that causethe foam to deteriorate over time.

The block diagram of FIG. 27 shows a sequence of actions similar tothose of FIG. 23 for making the life status assessment. The assessmentof FIG. 27 relies on a relaxation transient rather than the deformationtransient of FIG. 23. At block 320 a nonzero weight W is applied to themattress as a preparatory step. Block 322 establishes whether or not thedeformation transient associated with preparatory application of theweight is complete. At some time after the transient is considered to becomplete the weight is removed (block 324) with the time of removalbeing designated as t=0. The removal of the weight opens a measurementwindow during which the time of flight of one or more radar pulses isused at block 326 to establish how distance d changes due to relaxationof the foam components of the mattress. Block 328 establishes whether ornot the relaxation transient is complete. Once the relaxation transientis complete the measurement window closes and the method branches toblock 330 where remaining life is assessed as a function of the temporalprofile of the relaxation as already described in connection with FIGS.24-26, except that the temporal profile would be one in which dincreases with the passage of time. Of course, the preparatory weightapplication described in this paragraph and shown in FIG. 27, blocks320, 322 could be the weight application of FIG. 23, blocks 306, 310.That is, both a deformation test and a relaxation test could be carriedout sequentially.

The weight used when determining life status of the mattress byobserving a deformation transient or a relaxation transient may be aninanimate test weight. Alternatively the test weight may be the knownweight of the patient. In connection with any sequence of actions thatrequire knowledge of patient weight the weight of the patient may bedetermined in any suitable way. Among these are using the weight readingfrom a weight measuring system on board the bed, retrieving thepatient's weight automatically from an electronic health record, andreceiving a manual input from a caregiver or other user.

In general a method for determining the life status of a patient supportsurface includes measuring at least one physical parameter of thepatient support surface. “Physical parameter” includes the rate ofchange of a selected physical parameter). Examples of physicalparameters include thickness (e.g. distance d with or without weightapplied) time to compress or uncompress (i.e duration of a deformationor relaxation transient as explained in connection with the examples ofFIGS. 23-27). The method also includes comparing the physical parameterto a first, or physical parameter limit in order to assess life status.For example distance d can be compared to a lower limit and, if distanced is less than the limit, the mattress can be declared to have reachedthe end of its life.

The method may also include determining one or more derived parametersfrom the measured physical parameter or parameters, for example by wayof a lookup table or an equation expressing the derived parameter as afunction of the measured physical parameter. The method may then comparethe derived parameter to a second, or derived parameter limit in orderto assess life status.

The standalone RADAR apparatuses 12, 20, 22, 24 discussed above forretrofitting onto existing patient support systems or for use asmattress end-of-life testing, may be used with mattresses 100 ofdifferent types. Thus, in some embodiments, the housing of thestandalone RADAR apparatus 10, 20, 22, 24 has one or more inputs thatare used to select the type of mattress 100 with which the standaloneRADAR apparatus 12, 20, 22, 24 is to be used. Based on the selected typeof mattress, the appropriate TOF and/or distance thresholds are used inthe various manners described elsewhere herein. In some embodiments inwhich circuitry 24 of the standalone RADAR apparatus communicates withcircuitry 26 of the existing patient support system 10, inputs includedin the patient support apparatus 10 and coupled to circuitry 26 are usedto select the type of mattress being used.

Referring now to FIG. 12, an embodiment of patient support system 10 isdepicted in which RADAR antenna 12 a-g are coupled to a bottom surface138 of panels 132 of head, seat, and foot sections 122, 124, 128 ofmattress support deck 120. Except where noted below, the descriptionabove of the embodiment of FIG. 11a is equally applicable to theembodiment of FIG. 12, such as with regard to the placement of antennae12 a-g relative to the patient's bony prominences. Respective antennaefeeds 52 for each antennae 12 a-g are routed along bottom surface 138 toeach corresponding antennae 12 a-g. By placing antennae 12 a-g on thebottom surface 138 of panels 138, some of the blind range of eachantennae 12 a-g is taken up by the thickness of the panels 132. Thisallows the upper boundary of the blind range of RADAR antennae 12 a-g tobe moved further downwardly within mattress 100 toward its bottomticking layer 108 for a given pulse period as compared to the previouslydescribed embodiments in which antennae 12 are located inside of therespective mattress or on top surface 132 of panels 132 of deck 120.Alternatively, the period of pulse 14 can be made longer, if desired,and still have the upper boundary of the blind range at the same depthwithin mattress 100 as compared to the previously described embodiments.

As was the case with the embodiment of FIG. 11A, different types ofmattresses can be placed on deck 120 of the embodiment of FIG. 12 andthe impedance of impedance matching circuitry 22 adjusted accordingly.However, in the FIG. 12 arrangement having RADAR antennae 12 a-g coupledto bottom surface 138 of panels 132 of deck 120, pulse 14 and thereflected signal 18 also travel through panels 132. Thus, the impedanceof panels 132 contributes to the overall impedance of the environment towhich impedance matching circuitry 22 is to be matched. Furthermore, TOFand distance, d, thresholds for determining the bottoming out condition,for example, are established within the software of circuitry 24 and/orcircuitry 26 to account for the thickness of panels 132.

Referring now to FIG. 13, a bottom plan view of mattress support deck120 is shown. However, in the FIG. 13 embodiment, a movableantenna-support plate 140 is coupled to each of head, seat, and thighsections 122, 124, 128 and respective RADAR antennae 12 a-g are mountedto the respective plate 140. Specifically, RADAR antennae 12 a, 12 b aremounted to the plate 140 coupled to head section 122; RADAR antennae 12c, 12 d, 12 e are mounted to the plate 140 coupled to seat section 124;and RADAR antennae 12 f, 12 g are mounted to the plate 140 coupled tofoot section 128. As shown diagrammatically in FIG. 13, an actuator 142is provided on the bottom of each section 122, 124, 128 and is operableto move the respective plate 140, and therefore the RADAR antennae 12a-g supported by the respective plate 140, back and forth beneathsections 122, 124, 128 along the longitudinal dimension of deck 120 asindicated by double headed arrows 144.

Because different patients have different sizes and shapes, sometimesreferred to as patient morphology, the ability to move RADAR antennae 12a-g relative to deck 120 and therefore, relative to the overlyingmattress 100 and patient 16, allows RADAR antennae 12 a-g to bepositioned optimally beneath the patient where the patient's bonyprominences immerse into the mattress 100 by the greatest amount.Furthermore, moving plates 140 from one end of each section 122, 124,128 to the other end and taking TOF measurements and/or calculatingdistance, d, as the plates 140 move throughout their ranges of movement,allows an image to be made of the patient's immersion contour into themattress 100 in some embodiments.

Circuitry 26 is coupled to each actuator 142 and controls the operationof each actuator 142 to move the respective plate 140 in someembodiments. It is worth noting that the RADAR antennae 12 c-e on theplate 140 associated with seat section 124 are aligned in the lateraldimension of deck 120 rather than being arranged in the triangularpattern depicted in FIGS. 11A and 12. This is because during movement ofplate 140 of seat section 124, RADAR antenna 12 d will become positionedgenerally directly beneath the patient's coccyx at one position of plate140 and RADAR antennae 12 c, 12 e will become positioned generallydirectly beneath the patient's right and left iliac tuberosity atanother position of plate 140.

Referring now FIGS. 14-16, different examples of actuators 142 to moveplates 140 relative to deck 120 are shown. These are given asillustrative examples and, therefore, it should be appreciated thatother similar types of actuators may be used instead. In the descriptionthat follows with regard to FIGS. 14-16, actuators 142 as used on headsection 122 of deck 120 are discussed. However, the discussion ofactuators 142 as used on head section 122 is equally applicable to theuse of actuators 142 on seat section 124 and foot section 128, and alsoon thigh section 126 for those embodiments having a movable plate 140and one or more RADAR antennae 12 associated with thigh section 126.

As shown in the embodiment of FIG. 14, actuator 142 includes a threadedjack screw 146 and a motor 148 that operates through a gear reducer 150to turn jack screw 146 in first and second directions depending uponwhether plate 140 is to be moved toward a head end frame member 130 a offramework 130 or away from head end frame member 130 a. Motor 148 iscoupled to circuitry 26 of patient support system 10 to receive commandsignals therefrom. A threaded nut 149 is coupled to the undersurface ofplate 140 and extends downwardly therefrom. Jack screw 148 is threadedthrough nut 149. The threaded engagement between nut 149 and jack screw148 results in nut 149 and plate 140 moving along jack screw 148 whenjack screw is turned by the motor/gear reducer unit 148, 150. In theillustrative embodiment, gear box 150 is mounted to an inner side wallof frame member 130 a. Suitable fasteners such as screws may be providedfor this purpose. In other embodiments, gear box 150 and/or motor may bemounted to the overlying panel 132 either directly or via a bracket orthe like hanging downwardly from the overlying panel 132.

In the illustrative FIG. 14 example, guides 152 having C-shaped crosssections are attached to inner walls of respective side frame members130 b, 130 c of framework 130. End regions of plate 140 are receivedwithin the channels defined by the C-shaped guides 152. Thus, guides 152support the respective plate 140 for sliding movement relative to headsection 122 and constrain plate 140 to remain in its substantiallyparallel orientation with panel 132 of head section 122. Thus, thechannels defined by the C-shaped guides 152 are sized so that endsregions of plate 140 fit within the channels with a minimal amount ofclearance therebetween. In alternative embodiments, guides 152 areomitted and frame members 130 b, 13 c are configured with integralguides. For example, in some embodiments, the inner walls of framemembers 130 b, 130 c may have slots therethrough that are sized forreceipt of end regions of plate 140 therein. In other embodiments, theinner walls of frame members 130 b, 130 c themselves may be formed withgrooves to define C-shaped channels therein.

As is suggested in FIG. 14, the upper surface of plate 140 that carriesRADAR antennae 12 a, 12 b is spaced vertically downwardly by a slightdistance such as on the order of about ¼ inch to about 1 inch from thebottom surface of the overlying panel 132. Thus, an air gap betweenRADAR antennae 12 a, 12 b and panel 132 exists in the FIG. 13-16embodiments in which plates 140 are provided on deck 120. The air gapcontributes to the overall impedance of the environment to whichimpedance matching circuitry 22 is to be matched. It is known that freespace, such as that of the air gap, has an impedance of 377Ω. Thisdisclosure contemplates that RADAR antennae 12 may be supported up to 10cm or more below the upper surface 134 of deck 120.

Also, by placing antennae 12 a, 12 b on plate 140 with an air gapbetween plate 140 and panel 132, some of the blind range of each antenna12 a, 12 b is taken up by the air gap as well as the thickness of thepanels 132. This allows the upper boundary of the blind range of RADARantenna 12 a, 12 be to be moved even further downwardly within mattress100 toward its bottom ticking layer 108 for a given pulse period ascompared to the previously described embodiment of FIG. 12 in whichantennae 12 are located on the undersurface of panels 132 of deck 120.Alternatively with regard to the FIG. 13-16 embodiments, the period ofpulse 14 can be made longer, if desired, and still have the upperboundary of the blind range at the same depth within mattress 100 ascompared to the previously described embodiments.

As shown in the embodiment of FIG. 15, actuator 142 includes a flexibletether 154 (e.g., cable, band, belt, or chain) trained around amotorized drive wheel 156 (e.g., pulley or sprocket) and an idler wheel158 (e.g., pulley or sprocket). A motor 160 is mounted to frame member130 a and/or panel 132 and is operated under the control of circuitry 26of rotate drive wheel 156 in first and second opposite directionsdepending upon whether plate 140 is to be moved toward frame member 130a or away from frame member 130 a in the longitudinal dimension of headsection 122. An anchor 162 is provided to affix one flight of theflexible tether 154 to plate 140 such that rotation of the motorizeddrive wheel 156 by motor 160 moves the movable plate along the guides152. The axes about which drive wheel 156 and idler wheel 158 rotate isgenerally perpendicular to panel 132 and plate 140. The discussion aboveregarding alternative guides, impedance matching, and blind rangeboundary location in connection with the FIG. 14 embodiment is equallyapplicable to the FIG. 15 embodiment.

As shown in the embodiment of FIG. 16, actuator 142 includes amulti-stage scissors linkage 164 interconnected between end frame member130 a of head section 122 and movable plate 140. A motor 166 is mountedto the end frame member 130 a and/or panel 132 and is operable to pivota main link 168 of the scissors linkage 164 in first and second oppositedirections, as indicated by double headed arrow 170, to extend andretract the scissors linkage 164 to move the movable plate 140 along theguides 152 relative to panel 132. A first slider 172 is provided at thehead end of linkage 164 and a second slider 174 is provided at the footend of linkage 164. Slider 172 slides along a bail 176 and slider 174slides along plate 140 as scissors linkage 164 extends and retracts. Thediscussion above regarding alternative guides, impedance matching, andblind range boundary location in connection with the FIG. 14 embodimentis equally applicable to the FIG. 16 embodiment.

According to this disclosure, antennae 12 are tuned by impedancematching circuitry 22 to match the environment through which pulse 14and reflected signal 18 travel to the driver circuitry 20, which in someembodiments is typically about 50Ω to about 70Ω. In particular, antennae12 are tuned to the environment of patient support system 10. In thedisclosed embodiments, antennae 12 are not radiating entirely into freespace, but rather into a mattress and/or into a frame of patient supportsystem 10. Thus, in some embodiments, the antennae 12 are tuned to matchthe impedance of the mattress for the case of the in-mattress antennae12. In other embodiments, the antennae 12 are tuned to match theimpedance of the frame and mattress of patient support system 10 for thecase of the below-mattress antennae 12.

As mentioned above, some embodiments of the antennae 12 disclosed hereinexhibit the characteristic of circular polarization. However, it iswithin the scope of this disclosure for antennae 12 to be configured toexhibit the characteristic of horizontal, vertical, or ellipticalpolarization at the option of the designer.

In some embodiments, patient support system 10 may have an array ofantennae 12, all connected to one RADAR system 12, 20, 22, 24, andoptionally, the RADAR system may multiplex between the antennae 12 ofthe antenna array. Alternatively, the patient support system 10 may usean array of RADAR systems 12, 20, 22, 24, each with one or more antenna12. In some embodiments, the system 10 may use a bi-static RADAR system12, 20, 22 24.

In addition to the blind range issue that causes RADAR system 12, 20,22, 24 to not be able to see very close objects, RADAR system 12, 20,22, 24 also must deal with removing clutter from the reflected signal18. Clutter is created by objects that provide RADAR returns that areirrelevant. For example, return signals reflecting off of internalcomponents of the mattress or components of the frame of patient supportapparatus 10. In other words, return signals reflected by anything otherthan the target or object 16 of interest is considered to be unwantedclutter. Accordingly, circuitry 24 and/or circuitry 26 is programmed orconfigured to reduce the effects of clutter.

On way to reduce clutter is to use background subtraction to ignore theportions of the mattress and/or frame of patient support system 10 thatare not of interest. For example, RADAR system 12, 20, 22, 24 may beoperated to emit one or more pulses 14 and take a measurement of the oneor more reflected signals 18 when no patient 16 is present on thepatient support apparatus 10. The one or more reflected signals 18 underthese conditions represent a background signal which, in many instances,will be reflections from components that are different ranges than thepatient 16 will be. Circuitry 24 or circuitry 26 is programmed tosubtract the “no patient” reflected signal data from the reflectedsignal data when the patient 16 is on the mattress.

In some embodiments, circuitry 24 or circuitry 26 may be configured toimplement a pulse compression algorithm. By using pulse compression, theTOF or distance, d, to the target 16 can be determined even though thepulse is longer (i.e., pulse length (distance)=pulse length inseconds×speed of light) than the distance between RADAR antennae 12 andthe object 16. For example, pulse compression is one possible way ofdistinguishing between the RADAR pulse reflection 18 from the mattressand the RADAR pulse reflection 18 from the patient 16. These reflectionswill likely be so close together that the pulse length (in distance) islarger than the antenna-to-patient distance, d. Pulse compression may beaccomplished by frequency analysis such as by using linear modulation,non-linear modulation, or a coded waveform such as a Costas code andalso by phase modulation. It should be noted that use of pulsecompression will adversely effect the detection range of the RADARapparatus 12, 20, 22, 24 and so is only suitable for those embodimentsin which RADAR antennae 12 are located at a sufficient distance from thepatient 16 that the bottoming out condition or related thresholds arestill detectable or determinable despite the adverse effects.

Inherently, there is noise in the RADAR system 12, 20, 22, 24. Thus,each RADAR ranging sample provides an estimate of the distance, d, tothe patient 16 from the respective antenna 12. Assuming there is randomnoise, averaging the signals (e.g., TOF or distance, d) togetherprovides a better estimate of the actual distance, d, to the patient 16than a single ranging measurement. The averaging may be done bycircuitry 24 or circuitry 26 on the raw radar signal (average raw radardata, then use the averaged data to produce a range estimate) or on therange estimates (each radar ranging sample is used to create a rangeestimate, then many range estimates are averaged). The averaging may bedone in multiple steps, for example on the raw signal and subsequentlyon the range estimates. In some embodiments, oversampling (sample at arate higher than the Nyquist rate) is implemented by circuitry 24 orcircuitry 26 so that the signal observations are strongly correlated.

In some embodiments, circuitry 24 or circuitry 26 is programmed toimplement pulse-pair processing to determine what targets 16 (e.g.,which portions of the patient 16) are moving by comparing the phase ofsuccessive pulse pairs (i.e., the phase of successive reflected signals18). If there is an object 16 at a certain range that has no change inphase in successive reflected signals 18, it is considered clutter bycircuitry 24 or circuitry 26 and ignored. On the other hand, a patient16 who is breathing and has blood-mass movement due to the patient'sheartbeat will have a several degree phase shift at GHz frequenciesbetween successive reflected signals 18. Thus, if the phase of thereceived signals 18 are always the same, then the object from which thesignals 18 are reflected isn't moving and so the associated signals 18are ignored.

In some embodiments, circuitry 24 or circuitry 26 is programmed toimplement a Doppler filter. That is, the reflected signals 18 areprocessed to determine the magnitude of a Doppler shift and one or morefilters (e.g., software filters) are used to determine what data toinclude and what data to exclude from further analysis or processing.Only targets 16 producing a Doppler shift in the region or interest areconsidered. For example, if reflected signals 18 having a Doppler shiftof less than a first frequency, F1, and more than a second frequency,F2, are kept, then a band-pass filter is implemented. If reflectedsignals 18 having a Doppler shift less than a first frequency, F1, arekept, a low pass filter is implemented. Such a filter may be used tokeep the non-moving clutter for further use (e.g., backgroundsubtraction) or future analysis, if desire. If reflected signals 18having a Doppler shift more than a second frequency, F2, then a highpass filter is implemented.

In some embodiments, the at least one RADAR apparatus 12, 20, 22, 24and/or control circuitry 26 of patient support apparatus 10 isconfigured to determine a heart rate (HR) and/or a respiration rate (RR)of the patient. For example, the Doppler shift information justdescribed may be processed to determine the HR and the RR. Alternativelyor additionally, the circuitry 24 or circuitry 26 may implement aballistocardiography algorithm to determine the HR and the RR. Forexample, a first Doppler filter may be implemented by circuitry 24 orcircuitry 26 to detect chest movement due to a heartbeat of the patientto determine the HR. Similarly, a second Doppler filter may beimplemented by circuitry 24 or circuitry 26 to detect diaphragm movementof the patient to determine the RR. Thus, circuitry 24 or circuitry 26uses the Doppler shift information from signals 18 to determine the HRand the RR.

In some embodiments, RADAR antennae 12 are configured as an array ofRADAR antennae 12 as mentioned above. The array of RADAR antennae 12 mayinclude a phased-grid array of antennae 12, for example. A phased-gridarray of antennae 12 permits beam steering or beam forming of theemitted pulses 14 so that the pulses 14 are aimed at various portions ofthe target 16 that are not necessarily directly vertically above theemitting antennae 12, or stated more accurately, so that the emittedpulse 14 wave is at an angle other than 90 degrees to the plane definedby the one or more emitting antennae 12. The beam steering/forming maybe accomplished, for example, by adjusting the phase of the emittedpulses 14 of adjacent antenna 12 of the phased-grid array so that thepulses 14 are either more in phase or more out of phase so as to shapethe overall emitted pulse 14 beam. Changing the phase of the pulses 14of adjacent antennae 12 changes the direction and/or shape of the beamdefined by the emitted pulses 14. Because beam forming is based on phasedifferences, it works with narrow band signals. Furthermore, use of beamforming may improve the ranging accuracy by up to 1 cm at close range,such as in the patient support system 10 embodiments disclosed herein.Beam forming may also be accomplished by changing a distance betweenRADAR antennae 12 according to this disclosure.

Optionally, one or more RADAR lenses may be used with respective RADARantennae 12 to improve the ranging accuracy. A RADAR lens focuses theemitted pulse 14 wave to a more localized area of the target. It shouldbe noted that use of one or more RADAR lenses may be more appropriatefor the embodiments in which RADAR antennae 12 are outside of themattress, and particularly, in the embodiments of FIGS. 12-16 in whichRADAR antennae are beneath mattress support deck 120. This is becausethe thickness of the one or more RADAR lenses may possibly be felt bythe patient 16 if placed inside of a mattress. Known RADAR lensesinclude, for example, the Luneburg lens and the Maxwell's fish-eye lens.In some embodiment, RADAR antennae 12 may be carried by a respectivehousing that also carries the RADAR lens. Thus, each RADAR antenna,housing, and lens may be packaged together as a unit. A port forcoupling of the antenna feed 52, such as a coaxial cable, may beprovided on an external surface of the housing. Alternatively, theantenna feed 52 may include a short segment of cable that extends fromthe housing and that terminates at an electrical connector.

As noted above, the RADAR systems contemplated herein are capable ofdetermining a patient's heart rate and/or respiration rate. Thus, thepresent disclosure contemplates embodiments in which patient supportapparatus 10 includes patient support frame 110, patient support surface100 supported on the patient support frame 110, and a RADAR system 12,20, 21, 22, 24 carried by the patient support frame 110. The RADARsystem 12, 20, 21, 22, 24 is operable to determine a depth to which apatient is immersed into the patient support surface 100 and is alsooperable to perform a Doppler analysis to determine at least one of aheart rate or a respiration rate of the patient. In some embodiments,the RADAR system 12, 20, 21, 22, 24 is operable to determine both theheart rate and respiration rate of the patient.

The RADAR system 12, 20, 21, 22, 24 includes electronically steerableRADAR sensors, such as electronically steerable RADAR antennae, in someembodiments. For example, the electronically steerable RADAR sensorsinclude a plurality of transmitting antennae 12 a and a plurality ofreceiving antennae 12 b. The plurality of transmitting antennae 12 a andthe plurality of receiving antennae 12 b are arranged in a grid beneathan upper surface of the patient support surface 100.

In some embodiments, signals 18 received by the plurality of receivingantennae 12 b are used by the RADAR system 12, 20, 21, 22, 24 for bodycontour mapping. The body contour mapping may, in turn, be used bycircuitry 24, circuitry 26, and/or remote server 40, or some othercomputer device, to make one or more of a variety of subsequentdeterminations such as one or more of the following: determining whetherthe patient is at risk of developing pressure ulcers; determining aBraden score for the patient including determining a patient mobilitysub-factor of the Braden score; determining functional decline of thepatient; determining a location on the patient support surface of atleast one of the patient's legs, arms, trunk, pelvis or head;determining whether the patient is side-lying, lying on their stomach,or lying on their back; determining whether the patient has slid towarda foot end of the patient support surface or whether the patient is in aproper position on the patient support surface 100 of the patientsupport apparatus 10; determining sleep quality of the patient; ordetermining impending exit of the patient from the patient supportapparatus 10. Body contour mapping may also be useful in estimatingpatient weight. Such an estimate may be based exclusively on the bodycontour mapping, or may be based on body contour mapping and one or moreother parameters such as the patient's immersion.

In connection with determining the patient mobility sub-factor of theBraden score, the following numerical values are given: 1. CompletelyImmobile—the patient does not make even slight changes in body orextremity position without assistance; 2. Very Limited—the patient makesoccasional slight changes in body or extremity position but is unable tomake frequent or significant changes independently; 3. SlightlyLimited—the patient makes frequent though slight changes in body orextremity position independently; and 5. No Limitations—the patientmakes major and frequent changes in position without assistance.

In some embodiments, inflation of at least one air bladder 30 of one ormore air bladders 30 of the patient support surface 100 is adjustedbased on whether the patient is side-lying, lying on their stomach, orlying on their back as determined from the body contour mapping.Alternatively or additionally, inflation of at least one air bladder 30of one or more air bladders 30 of the patient support surface 100 isadjusted based on whether the patient has slid toward the foot end ofthe patient support surface 100 as determined from the body contourmapping. When it is stated herein that “inflation” of an air bladder is“adjusted,” both inflation of the air bladder (i.e., increasing pressureby adding air) and deflation of the air bladder (i.e., decreasingpressure by removing air) are covered by such language.

In some embodiments, the RADAR system 12, 20, 21, 22, 24 is operable todetermine a distance, d, to the patient 16 or to a surface 112 of thepatient support surface 100 adjacent the patient 16 for each receivingantenna 12 b of the plurality of receiving antennae 12 b by using (i) atime-of-flight (TOF) between transmission of pulses 14 from theplurality of transmitting antennae 12 a and receipt by the plurality ofreceiving antennae 12 b of the reflected signal 18 that is reflectedback from the patient 16 or reflected back from the surface 112 of thepatient support surface 100 adjacent the patient, (ii) antenna beamangle and geometry, and (iii) signal strength.

The present disclosure contemplates that the Doppler analysis todetermine at least one of a heart rate or a respiration rate of thepatient includes a micro-Doppler analysis that determines a phase changebetween first signals 14 that are transmitted by the plurality oftransmitting antennae 12 a and second signals 18 that are received bythe plurality of receiving antennae 12 b. The Doppler analysis is usedto determine one or more of the following: detection of a heart beat;premature ventricular contractions (PVC's) of the patient's heart;rate-based arrhythmias of the patient's heart; lethal arrhythmias of thepatient's heart; onset of congestive heart failure; or progression ofcongestive heart failure. Alternatively or additionally, the Doppleranalysis is used to detect apnea, including obstructive sleep apnea, ofthe patient.

Referring now to FIG. 18, one example of the RF driver/receivercircuitry 20 of one embodiment of a RADAR system for detecting apatient's heart beat and/or respiration includes a local oscillator (LO)180 which produces an output signal 182 that is communicated to an inputof a power splitter 184. In the illustrative example, signal 182 isoutput by LO 180 in the form a Sin(ωt) with a frequency of about 6GigaHertz (GHz) to about 18 GHz. Power splitter 184 has a first outputfrom which a first output signal 186 is communicated to transmittingantenna 12 a and power splitter 184 has a second output from which asecond output signal 188 is communicated to a local oscillator input (L)of a mixer 190. In the illustrative example, signals 186, 188 are eachof the form a/2×Sin(ωt). Thus, power splitter 190 splits signal 182 inhalf.

The transmitting antenna 12 a of FIG. 18 emits pulse 14 which isreflected by the target 16 as signal 18 which is, in turn, received bythe receiving antenna 12 b in a similar manner as described above inconnection with other embodiments. An output signal 192 from thereceiving antenna 12 b is input into a low-noise amplifier (LNA) 192 andan output signal 194 from the LNA 192 is communicated to a reflectedsignal input (R) of mixer 190. As indicated in block 196 of FIG. 18,signal 194 output from LNA 192 is of the form A×Sin(ωt+ϕt) whereϕ(t)=ϕo+4π/λ×x(t) and dϕ(t)/dt=4π/λ×dx/dt<<ω. In the foregoing formulae,ϕo is the (assumed static) phase offset of transmitting antenna 12 a toreceiving antenna 12 b due to transmission distance and dx is chest wallmovement due to breathing and heartbeat. The coefficient, A, includesthe gain of antennae 12 a, 12 b, target reflection coefficient, pathloss from transmitting antenna 12 a to receiving antenna 12 b, and LNAgain. The A coefficient is a lumped constant that may change (e.g., dueto insertion loss of mixer 190), but gain of the RADAR system is notrelevant in connection with determining the phase change due to Dopplershifting.

In the illustrative example, mixer 190 is a model no. IQ-0618 mixeravailable from Marki Microwave, Inc. of Morgan Hill, Calif. As notedabove the L input of mixer 190 receives signal 188 from power splitter188 and the R input of mixer 190 receives signal 194 from LNA 192. Asindicated by the text “Want PL>>PR” in mixer block 190, it is desirablethat the power level of signal 188 at the L input of mixer 190 be muchgreater than the power level of signal 194 at the R input of mixer 190,such as on the order of ten times greater for example. Mixer 190produces a quadrature signal 198 at a Q output of the mixer 190 and anin-phase signal 200 at an I output of the mixer 190.

As indicated in block 204 of FIG. 18, the in-phase signal 200 is of theform A×Sin(ωt+ϕ(t))×Sin(ωt) which is equal toA×[Cos(2ωt+ϕ(t))+Cos(ϕ(t))]. As indicated in block 202 of FIG. 18, thequadrature signal 198 is of the form A×Cos(ωt+ϕ(t))×Sin(ωt) which isequal to A×[Sin(2ωt+ϕ(t))+Sin(ϕ(t))] due to the +90 degree phase shifton the Q signal 198 as compared to the I signal 200. A first low passfilter (LPF) 206 of the RADAR system of FIG. 18 has an input thatreceives the quadrature signal 198 from the Q output of the mixer 190and a second low pass filter (LPF) 208 of the RADAR system of FIG. 18has an input that receives the in-phase signal 200 from the I output ofmixer 190. In the illustrative example, each LPF has a cutoff frequencythat is set to about 100 Hz but LPF's having cutoff frequencies in therange of about 2,000 kilohertz (kHz) to about 10 Hz are also believed tobe suitable.

An output signal 210 from the first LPF 206 is input into a firstanalog-to-digital (A/D) converter 212 for the quadrature channel and anoutput signal 214 from the second LPF 208 is input into a second A/Dconverter 216 for the in-phase channel. The output signal 210 is of theform Sin(ϕ(t)) and the output signal 214 is of the form Cos(ϕ(t)). Thus,the LPF's 206, 208 filter out the 2ωt+ϕ(t) component of respectivequadrature and in-phase signals 198, 200. As indicated at block 218 ofFIG. 18, the digital Q and I outputs of respective A/D converters 212,216 are processed, such as by circuitry 24 in some embodiments, todetermine ϕ(t) and x(t) by using the formulae ϕ(t)=atan(Q/I)=ϕo+4π/λ×x(t) and x(t)=λ/(4π)×(a tan(Q/I)−ϕo).

It is recognized by those familiar in the art that the features of theblock diagram may be implemented using elements on a printed circuitboard, for example a Microsemi MDU1020 series planar transceiver, whichis an X-band motion detector that utilizes Doppler shift phenomenon tosense motion. As a specific example, for narrow band RADARs, a 90-degreephase shift may be implemented with a length of transmission line thatis one-quarter wavelength long. Similarly, the features indicated inFIG. 18 may be implemented as a system on chip, for example an AWR1642single-chip RADAR sensor manufactured by Texas Instruments.

By taking distance measurements, x(t), over time, a displacement graphis generated for one or more locations on a grid at which the steerableradar sensors (e.g., antenna 12 a, 12 b) are aimed or focused. Toproduce the patient's heart beat signal and to determine the patient'sheart rate and respiration rate, averaging and filtering algorithms areimplemented for selected displacement measurements, x(t), such as thosein which one or more radar sensors are aimed at the patient's upperthorax region. Furthermore, the x(t) measurements for all locations onthe grid can be used to generate a body contour map. The grid may beestablished by X and Y coordinates on a reference plane which, ifdesired, can correspond to an upper surface of the mattress 100 in whichcase displacement x(t) is measured downwardly from the reference planeat each grid point due to immersion of the patient into the mattress100. Alternatively, the reference plane may correspond to the uppersurfaces of antennae 12 a, 12 b that are located within or beneath themattress 100 in which case distance, d, upwardly from the referenceplane to the object 16 is adjusted at each X-Y grid location based onthe x(t) measurements. It should be appreciated that distancemeasurements, x(t), appearing in FIG. 18 and referenced above,correspond to movement in the Z direction (e.g., generally vertical) ifthe X-Y reference plane is established as a generally horizontal plane.

Referring now to FIG. 19, an upper graph 220 shows an example of a traceor graph from an electrocardiograph (EKG) with the x-axis of graph 220being time in seconds and the y-axis being analog to digital converter(ADC) counts. The ADC counts is a normalized value representing ameasured voltage of the electrical activity of a beating heart. A lowergraph 224 of FIG. 19 is the phase, ϕ(t), as determined by the system 20of FIG. 18. Graph 224 is generated, in some embodiments, based onmeasurements from a single radar sensor (e.g., single antenna pair 12 a,12 b) being aimed at a patient's chest continuously or at least for anextended period of time. In lower graph 224, the x-axis is time inseconds and corresponds to the x-axis of upper graph 220 and the y-axisis phase in degrees. A series of double headed arrows 222 in FIG. 19show that R-wave spikes in the upper graph 220 coincide with phasespikes of the lower graph. Thus, the spikes corresponding to the R-wavesin the measured phase, ϕ(t), can be used to calculate the patient'sheart rate.

A patient support system may benefit from the presence of RadioFrequency Identification (RFID) capability. The RFID capability may beof value in connection with making determinations of life status,monitoring patient immersion and maintaining patient immersion within adesired tolerance range. The life status may be expressed as a lifeparameter such as a quantification of life remaining, a quantificationof life expended, or may be an expression that indicates life status ina nonquantified way as described in more detail below in connection withFIG. 35. The examples given below in the context of the RFID capableembodiments are prophetic examples.

Referring to FIG. 28, a patient support system 10 includes a frame 110.Load cells 340, which are typically positioned near the four corners ofthe frame, are provided as part of a load measuring system to facilitatedetermination of the patient's weight. The load measuring systemincludes software which converts signals from the load cells to patientweight in, for example, pounds or kilograms.

The patient support system also includes a core support structure 344,such as a mattress, having an upper surface 346 and a lower surface 348.Supportive components of the core support structure include supportivefoam 350, but may also include other supportive components such aspressurizable bladders. The foam is described as supportive because itbears at least some of the weight of a patient who occupies the patientsupport. A ticking 354 envelopes the core support structure.

The patient support system also includes one or more radar systems 12,20, 22, 24 including at least one radar antenna 12 adapted to emit aradar pulse, and circuitry 20, 22, 24, and any software, all aspreviously described. The antenna is situated beneath upper surface 346and is spatially separated therefrom, for example by distance d. In theembodiment of FIG. 28 the radar system is shown as completely outsidethe core support structure and ticking. In another embodiment (FIG. 29)the radar system is inside the ticking. In yet other embodiments theradar system components may be distributed—some inside the ticking andsome not. For example in FIG. 30 antenna 12 is sandwiched between theticking and the core while circuitry 20, 22, 24 is outside the ticking.

In operation, the pulse emitted from the radar travels through thesupport structure and is reflected by either the upper surface 346 or asurrogate thereof. The pulse is a finite duration signal having a shapeand a frequency content. The pulse may be phase modulated, amplitudemodulated or frequency modulated. The reflected signal propagates backto antenna 12. In the interest of economy of expression, the emittedpulse and the reflected signal, taken collectively, are referred toherein as a ranging signal. The ranging signal, although useful fordetermining the range of a target, may be employed for other purposes aswell despite the selection of the modifier “ranging”. As describedabove, the time of flight of the ranging signal from the antenna, to thetarget, and back to the antenna may be used to estimate the distance dfrom the antenna to the target.

The “surrogate” referred to above accounts for the possibility thatupper surface 346 may not be radar reflective. The surrogate stands infor the upper surface, and therefore may be anything that reflects theemitted pulse and is spatially separated from the antenna bysubstantially the same distance as the upper surface is spatiallyseparated from the antenna. The “substantially the same” criterion meansthat the time of flight of the ranging signal with respect to thesurrogate and the time of flight of the ranging signal with respect tothe upper surface 346 would be equal or nearly equal. Therefore anydetermination of patient immersion or determination of a life parameterLP of the core based on the surrogate would not differ by any meaningfulamounts from determinations based instead on reflection from the uppersurface 346. One example surrogate is a radar reflective coating 356(FIG. 28) on the inner surface of the top portion of the ticking.Another example is the patient when supported by the core supportstructure.

Referring additionally to FIG. 31, the patient support system alsoincludes circuitry and/or algorithms 360 which determines a lifeparameter LP of the core support structure as a function of the rangingsignal. The algorithms may be coded in instructions which are held in amemory and executed by processor circuitry. In the interest of economyof expression, the foregoing phrase “circuitry . . . and/or algorithms”will be condensed to “circuitry”. The phrase “ranging signal” includesthe properties of the ranging signal such as its TOF or the distance ittravels from antenna to its target and back. The life parameter may bedetermined by processor circuitry which is on board the mattress 100 orthe frame 110, but which may also be at some other location including aremote location.

As shown in FIG. 31, the life determination circuitry may be packagedtogether with the impedance matching circuitry 22, with thedriver/receiver circuitry 20, with the processor circuitry 24, with thepatient support system circuitry 26, with an integrated circuit whichincludes the impedance matching circuitry 22, driver/receiver circuitry20, and processor circuitry 24, with other circuitry which happens to bepresent, or as stand-alone circuitry.

The patient support system also includes a Radio FrequencyIdentification (RFID) tag 364 having a memory 366. The RFID tag is incommunication with life determination circuitry 360. Certain informationsuch as model and serial number of the core support structure, and itsdate of manufacture may be preloaded into the RFID memory by themanufacturer. Other information may be entered by the user. Examples ofsuch other information include dates of entry into actual service anddates taken out of service. Yet other information may be written to theRFID at various times during service of the core support structure. Aswill be described in more detail below, the contents of the RFID memorymay be used for a variety of purposes such as to assist in determiningthe life parameter of the core support structure at a given point in itslifetime.

The patient support system also includes an RFID reader 370. In someembodiments the RFID reader is a component of frame 110 as seen in FIGS.28-30. In other embodiments the RFID reader is packaged as a componentof the core support structure analogous to the way radar system 12, 20,22, 24 is inside the ticking and immersed or embedded in the supportivefoam in FIG. 29. In other embodiments the RFID reader is an independentcomponent, for example a portable reader 370 (FIG. 32) that a user maycarry from place to place.

FIG. 33 is a block diagram showing one example of RFID tag 364 in use.FIG. 34 is a schematic of the involved components. Block 380 shows aproperty of the ranging signal being acquired. Block 382 shows circuitry360 determining the core support structure life parameter as a functionof the ranging signal. Block 384 shows the circuitry interacting withRFID tag 364 by writing information to its memory 366. The informationwritten to memory includes at least life parameter LP. The informationalso may include a property of the ranging signal (e.g. TOF, d). Theinformation may also include a time stamp TS revealing the timecorresponding to the life determination, for example Nov. 13, 2018 at11:53 PM. After information has been written to memory 366 the RFIDreader can interrogate the tag to extract the life determination fromthe memory.

FIG. 35 is a diagram showing examples of life parameters that may beuseful for indicating the life status of the core support structure, andhow the life parameters may be determined as a function of the rangingsignal or a property thereof. In the examples, distance d is compared toseveral life parameter thresholds labeled A through F. Pairs ofthresholds define various life status bands, for example slightly used(SU), moderately used (MU), heavily used (HU), end of life imminent(EOLI), and life exceeded (LE). The numerical scales show distance d(indicating the thickness of the core support structure), percentage oflife expended, and percentage life remaining. The expended and remaininglife percentages and threshold B shown in the example of FIG. 35 arebased on the a judgement that if d is four distance units or less thecore support structure has reached the end of its useful lifetime. Theinformation written to RFID memory includes at least the life parameterand may include other information such as the property of the rangingsignal (e.g TOF or d) and a time stamp TS.

FIG. 36 is a flow chart showing another example of the use of and theutility of RFID tag 364. In the example of FIG. 36, the circuitrydetermines the life parameter as function of A) a property of a firstranging signal and an associated first time stamp, both of which arewritten to the RFID memory, and B) a property of a second ranging signaland an associated second time stamp which is later than the first timestamp. More specifically, at block 390 ranging signal S1 is acquired ata time t1. At block 392 a property P1 of the ranging signal (e.g.distance d or its TOF) is determined. At block 394 the circuitryinteracts with RFID tag 364 by writing information to its memory 366.The information written to memory includes at least property P1 and itsassociated time stamp TS1.

At block 396 ranging signal S2 is acquired at a time t2 which is laterthan t1. In other words the ranging signals used at times t1 and t2 areattributable to distinct radar pulses from antenna 12. Given that theobjective is to assess the life status of the core support structure, t2can be selected to be long enough after t1 that some noticeabledeterioration of the core support structure can be expected to haveoccurred. At block 398 a property P2 of the ranging signal of block 396(e.g. distance d or its TOF) is determined. At block 400 life propertyLP is determined as a function of P1 and P2.

Continuing to refer to FIG. 36, it is evident that the ranging signalproperties of blocks 392 and 398 cannot be determined until afteracquisition of the corresponding ranging signals themselves at blocks390, 396. In addition, writing the signal properties to memory (blocks394, 402) cannot occur until the ranging signal properties is known(blocks 392, 398). However the actions of blocks 396, 398, can becarried out mostly in parallel with the actions of blocks 390, 392, 394subject to the constraint that acquisition step 396 must occur later intime than acquisition step 390.

Referring to block 400 of FIG. 36 and additionally to FIG. 37, propertyP2, and time stamp TS2 can be used along with property P1 and time stampTS1 previously written to memory at block 394 in order to understand howthe life parameter of the core support structure is changing over time.In principal there is no need to write P2 and TS2 to memory. Howeveraccumulating data at various times during the lifespan of the coresupport structure results in the development of a usage log in the RFIDmemory. Accordingly, FIG. 36 includes, at block 402, the option ofwriting LP2 and TS2 to the RFID memory. Other information, such as thelife parameter, can also be written to memory.

FIG. 38 shows one example of a usage log. The example usage log includestime stamps (shown as date only), at least one life parameter (remaininglife), distance d, and a calculated rate of deterioration (change inlife parameter per unit time) between successive time stamps. The usagelog data can be retrieved to assist in assessing the life status andunderstanding the deterioration characteristics of the core supportstructure. For example FIG. 39 shows the deterioration profile of thecore support surface (remaining life versus time stamp) based on thedata from the usage log. FIG. 40 shows the deterioration rate versustime stamp based on the data from the usage log. By way of example only,a person examining the information display of FIG. 40 might concludethat the core support apparatus deteriorated somewhat rapidly during aninitial break in period, then entered a phase of approximately constantdeterioration rate, then entered a phase of rapid deterioration, andfinally deteriorated somewhat slowly, perhaps asymptotically, near theend of its useful life.

The usage log can contain information about multiple mattresses. In thatcase, the contents of a usage log can be used to determine the relativeimportance of various factors in determining mattress life. Theimportance of a factor influences the weighting of that factor in anend-of-life prediction algorithm. In addition recorded information frommultiple mattress may be used to improve the algorithms associated withmattress life and patient immersion assessments.

The actions of determining a life parameter LP (FIG. 33, block 382; FIG.36 blocks 392, 398) may be carried out using any of the methodspreviously described. These methods include:

-   -   1) observing a ranging signal property such as distance d before        and after application of a known test weight;    -   2) observing a ranging signal property such as distance d at        various points in the lifespan of the core support structure        with no weight applied;    -   3) observing distance d at various points in the lifespan of the        core support structure with patient weight applied (which may be        thought of as a variant of method (1) carried out over a longer        time interval and without control over the amount of weight        applied);    -   4) observing the dynamic behavior of the core support structure        in response to application or removal of a test weight, which        may be patient weight.

It is therefore evident that in some embodiments A) the first time stampand its associated ranging signal property are determined at first knownload condition, and B) the second time stamp and its associated rangingsignal property are determined at second known load condition which isthe same as the first known load condition. In some embodiments thefirst and second known load conditions may both be zero load conditions.In other embodiments the first and second known load conditions are bothconditions of equal non-zero loads or are loads subsumed under a commonweight class as explained in connection with FIG. 20. Nonzero loads maybe the weight of one or more inanimate test weights or may be a patientweight.

The time stamps and life parameters of the example usage log of FIG. 38are not related to any particular event that might have a bearing on thelife parameter. By contrast, FIG. 41 shows a usage log whose entries arerelated to events that have a bearing on the life parameter. Each entryof the example usage log corresponds to the emission of a radar pulseand the determination of a life parameter (e.g. life remaining) at timeswhen a load, specifically patient weight, is applied to the core supportstructure and at times when patient weight is removed from the coresupport structure. Log entries may be made at other times as well.Knowledge of the loading history enables correlation of thedeterioration profile of the core support structure with loading (e.g.patient weight) history, and therefore may be more meaningful than adeterioration profile which is not linked to actual usage of the coresupport structure.

Continuing to refer to the usage log of FIG. 41, the patient weights W1,W2, W3 may be the weights of different patients. In other words apatient PA whose weight is W1 might have been assigned to the coresupport structure from TS1 to TS2 (e.g. January 4 at 3:22 PM to January5 at 11:00 AM). A patient PB whose weight is W3 might have been assignedto the core support structure from TS3 to TS2 (e.g. January 6 at 1:12 AMto January 8 at 9:00 AM). A patient PC whose weight is W5 might havebeen assigned to the core support structure from TS5 to TS6 (e.g.January 6 at 11:11 AM to January 10 at 8:00 AM). These example timeintervals do not account for time that the patient (PA, PB, or PCdepending on the time interval) may not have actually been occupying thecore support structure. In another example W1, W2 and W3 are weights ofthe same patient, which may or may not have changed over time. Theintervals of zero load represent that patient's absences from the coresupport structure during his hospital stay, for example to use thebathroom, to attend physical therapy, or to undergo a radiologicalprocedure.

Referring back to FIG. 36 it can be appreciated that in general thecircuitry determines the life parameter as function of a common rangingsignal property associated with each of the N time stamps where N≥2.“Common” means that the ranging signal property selected to beassociated with any particular time stamp is also the property selectedto be associated with all the other time stamps. For example ToF may beselected to be associated with all the time stamps, or distance d may beselected to be associated with all the time stamps, however ToF wouldnot be selected to be associated with some time stamps and distance dselected to be associated with the other time stamps.

The RFID capability of RFID-enabled embodiments may also be useful inconnection with monitoring patient immersion and maintaining immersionbetween upper and lower limits. For example immersion information can bewritten to the RFID memory from time to time and used for a variety ofpurposes. Among these are documenting the immersion of differentpatients, documenting the immersion of patients of different weights,and documenting the performance of immersion management system thatoperates to maintain the patient's immersion between upper and lowerlimits.

Another aspect of radar system 12, 20, 22, 24, involves eliminating ormitigating the effect of what is known as the direct path. Furtherdiscussion of the direct path and mitigating its effects are describedbelow.

A two-antenna radar includes a transmitting (Tx) antenna Tx and areceiving antenna Rx. Energy emitted from Tx propagates to the target.Energy reflected from the target propagates back to Rx. Thisemission/echo path has the information of interest. Energy emitted fromTx also propagates directly from Tx to Rx antenna and creates noise forthe system. This is referred to as the direct path.

In a system as described in this specification, the Tx and Rx antennasmay be so close to each other that the pulse emitted from Tx will bereceived by the Rx antenna along the direct path. Therefore, thesignal-to-noise ratio may be a problem if the direct path andemission/echo path pulses arrive at the Tx antenna simultaneously. Sinceradar uses the time from transmitting a pulse to the time of receipt ofa pulse to determine range, if the direct path pulse is incorrectlyclassified as the pulse reflected from the target, an erroneous rangeestimate will result.

One way to mitigate the effect of the direct path is to polarize theemitted energy and to use a receiving antenna not designed to respond tothe polarization state of the emitted pulse. For example, if the systemtransmits an RHCP (right hand circularly polarized) signal, the emittedsignal is “seen” as an RHCP signal when received at the target. But uponreflection from the target the RHCP signal becomes a left handcircularly polarized (LHCP) signal. If the Rx antenna is designed torespond to LHCP signals, it will detect the LHCP signals and ignore theRHCP direct path signals.

Another way to mitigate the effect of the direct path is to place aphysical barrier, possibly one that is conductive and/or grounded,between the Tx and Rx antennas. Doing so will attenuate the direct-pathsignal. The physical barrier may surround the Tx antenna and/or the Rxantenna.

Another way to mitigate the effect of the direct path is to design theTx and Rx antennas to have low gain in direction of the direct path andhigh gain in the direction of the expected target. This design mayinclude the use of an antenna array. By varying the phase of the signalto various antenna elements, the direction of the lobes and nulls may beadjusted.

Another way to mitigate the effect of the direct path is to employsoftware methods to filter out the signal of interest from the directpath signal. For example, because the range between the Tx and Rxantennas is fixed, say at 3 cm, then data from that range could befiltered out. Also, because of the fixed range, the Doppler shift alongthe direct path will always be 0. Accordingly, a Doppler filter may beused to detect/suppress data from the direct path.

Another way to mitigate the effect of the direct path is to use digitalsignal processing to reduce the direct signal. A non-limiting example isusing a direct signal cancellation (DSC) algorithm such as the ExtensiveCancellation Algorithm. In the DSC method, there are two receivingantennas: a first antenna aimed at the target and a second antenna aimedat the transmitting antenna. The first antenna receives some of thetransmitted signal. The first antenna receives a signal from the target,and this signal is compared to the signal received by the second antennato identify bistatic range and Doppler frequencies of the targets.Direct signal cancellation uses a least mean squares method (see R.Cardinali, F. Colone, C. Ferretti, and P. Lumbardo, “Comparison ofClutter and Multipath Cancellation Techniques for Passive Radar”, IEEERadar Conference 2007, pages 469-474, April 2007, and W. L. Melvin andJ. A. Scheer, “Principles of Modern Radar, Advanced Techniques”, volume2, chapter 17.3, SciTech Publishing, 2013), computes the complexweighting factors that are applied to the second antenna's signal, andsubtracts these weighted signals from the first antenna's signal withdifferent time delays.

Although certain illustrative embodiments have been described in detailabove, variations and modifications exist within the scope and spirit ofthis disclosure as described and as defined in the following claims. Forexample, radar is used in the foregoing examples, however other rangingtechnologies such as SONAR, LIDAR, and ultrasouound may be used.

The invention claimed is:
 1. A patient support system for supporting apatient, the patient support system comprising: a core support structurewhich includes supportive foam, the support structure having an uppersurface and a lower surface; a radar apparatus including at least oneradar antenna situated beneath the upper surface and spatially separatedtherefrom, the at least one antenna adapted to emit a pulse whichtravels through the support structure and is reflected, by either theupper surface or a surrogate thereof, as a reflected signal back to theat least one radar antenna, the emitted pulse and reflected signalcomprising a ranging signal; circuitry that determines a life parameterof the core support structure as a function of at least the rangingsignal; and an RFID tag having a memory, the RFID tag being incommunication with the circuitry.
 2. The patient support system of claim1 wherein the circuitry: A) determines the life parameter of the coresupport structure as a function of time of flight (TOF) of the rangingsignal; and B) interacts with the RFID memory.
 3. The patient supportsystem of claim 2 wherein the circuitry interacts with the memory bywriting at least the determined life parameter to the memory.
 4. Thepatient support system of claim 1 wherein the circuitry determines thelife parameter of the core support structure as a function of theranging signal and information content of the RFID memory.
 5. Thepatient support system of claim of claim 4 wherein the life parameter isremaining life of the core support structure.
 6. The patient supportsystem of claim 4 wherein the circuitry determines the life parameter asa function of TOF of the ranging signal.
 7. The patient support systemof claim 4 wherein the circuitry determines the life parameter asfunction of N time stamps (N≥2) and a common ranging signal propertyassociated with each of the N time stamps.
 8. The patient support systemof claim 4 wherein the circuitry determines the life parameter asfunction of: A) a first time stamp and an associated ranging signalproperty present in the RFID memory, and B) a second time stamp which islater than the first time stamp and a ranging signal property associatedwith the second time stamp.
 9. The patient support system of claim 8wherein the second time stamp and its associated ranging signal propertyare written to the RFID memory.
 10. The patient support system of claim8 wherein: A) the first time stamp and its associated ranging signalproperty are determined at first known load condition, and B) the secondtime stamp and its associated ranging signal property are determined atsecond known load condition which is the same as the first known loadcondition.
 11. The patient support system of claim 10 wherein the firstand second known load conditions are both zero load conditions.
 12. Thepatient support system of claim 10 wherein the first and second knownload conditions are both conditions of equal non-zero loads or loadssubsumed under a common load class.
 13. The patient support system ofclaim 12 wherein each nonzero load is the weight of one or moreinanimate test weights.
 14. The patient support system of claim 12wherein each nonzero load is the weight of a specific patient supportedon the core support structure.
 15. The patient support system of claim 4wherein the circuitry determines the life parameter as a function of adistance d traveled by the ranging signal during its TOF.
 16. Thepatient support system of claim 15 wherein the weight of the specificpatient is determined from at least one of: A) a user input, B) a loadmeasuring system of a frame that supports the core support structure, C)an electronic health record.
 17. The patient support system of claim 4wherein the RFID memory includes a usage log serving as a repository fordata which includes a magnitude of load applied to the support surface,a first time stamp associated with the applied load, a magnitude of aload removed from the support surface, and a second time stampassociated with the removed load.
 18. The patient support system ofclaim 1 wherein the surrogate is a patient supported by the supportsurface.
 19. The patient support system of claim 1 including an RFIDreader.
 20. The patient support system of claim 19 including a framethat supports the core support structure, and wherein the RFID reader isa component of the core support structure.
 21. The patient supportsystem of claim 20 wherein the RFID reader is a component of the frame.22. The patient support system of claim 19 wherein the RFID reader is anindependent component.
 23. The patient support system of claim 1including hardware, software or both for mitigating effects of a directpath between a radar transmitting antenna and a radar receiving antenna.